MicrostockGroup

In yesterday's film cameras, yes they would be exactly the same.  The camera just opens in the light to the film.  With cheap film vs expensive film though you will see a difference.

Today, the film is part of the camera so yes - the camera has a lot to do with the picture quality.  If a Canon Rebel series camera had the same sensor as a 1Ds series camera then yes, the pictures would be identical.  The 1D series cameras have a full frame sensor though giving them a less noisy image, better focus.  When the camera was made (ie: the sensor technology) also has a lot to do with it though - not just the model.  I would guess that a new rebel takes a far better pictures than the first 1DS camera in regards to noise, color, light levels.

Apart from controls, different cameras are like films: different grains, quality, saturation, color.  

Lens quality, yesterday and today, affect optical aspects of an image: focus, sharpness, CA, vignetting, etc.

I'd agree that both are important. I would add that an investment in a good lens is one you can reap benefits from over several camera bodies, so sometimes I look at the lenses as my long term investment and cameras are shorter term.

The other comment is that image quality - even with a great camera and great lens - can be significantly affected by the skill (or lack thereof) of the photographer. I've seen a lot of 5D2 owners in IS's critique forum who can't see why they can't just point their lovely camera and lens at anything and get a wonderful image as a result. This has always been true, but some of the spectacular advances in sensor and DSLR capture technology have encouraged people to become over optimistic about the role of great equipment.

It's both. Although I'd lean toward the lens as the most important part.

My 5DMII's image quality and output is totally different than the D300 I owned before it.

And different lenses produce different degrees of results. While you can measure sharpness and contrast, some lenses seem to have that magic output that others don't.

This is all too true. A top lens and a top cam make your job as a photographer even more critical. When I first used my 5D-II + 24-70/2.8 (a top lens) I was exited about the focusing and the exposure. After some pixel-peeping, I had to revert to my old method of all-manual, select 1 focus point, and use the monopod.
I prefer to chose my focus point myself, and also to slightly over-expose since the D5-II has a lot of headroom in the raw and all noise is gone in black hair this way.
The monopod is essential, except outdoors in bright tropical light > 1/500. The 24-70 is a very heave lens, heaver than the cam, and difficult to use handheld at lower exposures. Every little motion blur you will see on a 21MP cam and with a top lens. My carbon Manfrotto monopod is actually my best accessory.

Events are totally different than outdoor shoots and studio. I think for events and high ISO, a Nikon D700 is ideal, with its large sensor at just 12MP. I only do outdoors and studio, 100 ISO. My lightboxes allow F13 then. I tried 500 ISO in a mall with the D5-II, and the noise is great, but not up to stock standards, IMHO.

Trust me, from my time as a reviewer, I know it is mainly the photographer. I found it almost incomprehensible how some contributors could produce truly awful images, both technically and aesthetically, whilst using the latest and best equipment. Conversely I know one particular contributor who sold over 100K images on IS before bothering to upgrade from a 2003 Rebel Mk1 + kit lens combo. Just the photographer's post-processing skills alone will usually make more of a difference to the quality and visual impact of the final image than the sensor or lens.

Let's go back to the OP's opening statement of "I’ve always been a firm believer that 90% of your image quality comes from your lens". Personally I believe that 90% of image quality actually comes from the photographer, assuming of course that you have at least basic DSLR equipment with which to use.

Obviously, because this is a microstock forum, I'm assuming that the OP's question was geared towards producing microstock images. Although I have a 22MP camera it is still the case that about 98% of my sales on IS are at Large size (5MP) or smaller. I think better lenses and sensors allow you to actually capture images in marginally less favourable conditions than you could do so with poorer equipment __ not so much about quality specifically. Although I've got pro lenses that theoretically allow me to shoot at f2 or less, if I do so then the DoF is so shallow that the results are unlikely to be useable for stock.

In my experience if you're shooting for microstock then you basically need optimum conditions or you might as well not bother. Even if you get images captured in sub-optimum conditions accepted then it is unlikely they will sell much unless they are truly unique __ and that's a relatively rare circumstance. If you are shooting under studio/controlled/perfect situations, which probably 90%+ of successful microstock images are, then at say f8+ you probably won't be able to tell much difference between a pro lens and a kit lens.

The one area where the lens really is everything is the long-range telescopic stuff like sports and wildlife __ but you're probably not going to recover your outlay let alone make a living on microstock shooting that.

its AND logic, from the pure technical standpoint good photos need a good back AND good lens, but still plenty of scope for operator error

Both are important, but for perhaps the past 2 or 3 years I think the spotlight has shifted back onto the lens more than it was with the early generations of DSLRs

before 10MP came along it was mainly camera body that made the difference (less noise etc, resolution mattered a lot etc) and any old lens would take a similar quality of image as the camera could not resolve a high enough resolution to see all the imperfections of the cheaper lenses. yes faster glass would get push the limit some more, and cheaper lenses would distort more etc but body made the biggest difference

I'm still at 10MP D200, but I know that my better lenses can take better pictures if i got a new back because I can only spot an image taken with the cheap(ish) wide angle zoom that I have, I can't see much difference between my other primes or even the 70-300 if used at sensible lens angles and their best apertures

I would add an editing software to the end.
I think the order of importance would be; photographer, composition, model, lens, camera, editing software.

Kone