But the principles are still the same

I shoot Canon because..... well when I was switching from manual focus to auto focus ( many years ago) the Canon lens were silent, Nikons made noise. That was the only difference at the time... and now neither or any other DSLR is different enough to change manufacture.... Really there isn't a camera maker making bad gear these days... they can't afford to.

I am staying with Canon mainly because this is what I (or better: we, as my wife shoots with Canon as well) had from the start. We bought our first digital SLR in 2003 when, the Canon 300D was more or less the only affordable model. Over time we upgraded (30D, 1DMkIIn, 1DMkIV) and added a lot of glass.
Now a switch to another manufacturer would mean we had to replace all those lenses - that's the main reason I don't even look at Nikon for new cameras.
And one additional point: I am now using a 1DMkIV. I fully believe the capabilities of that camera are far beyond my own capabilities. Hoping to improve my photography by switching to another camera body is completely pointless. I'd rather invest the time improving my own skills. My camera is not the limiting factor.