Every microstock site will continue to take quality both in terms of technical excellence and image subject because they have no reason not too, to think otherwise is just completely daft. Quality has, does & always will be accepted and sell.
A lot of microstock sites have stopped accepting the crap they used to, that's all that has changed.
100% agreed, and phrased better than I could have put it.

I'm fine with the increased quality standards, and as someone who also buys microstock images, I'm glad some effort is being put into raising the bar on quality. A lot of crap (especially in the vector categories) has gotten into the collections, and it's a real effort to dig through some of the garbage to find usable images. If it's harder to get images accepted at istock now, I say good, and it should always get harder. If your work is worth buying, it will continue to get accepted. I think microstock agencies are just cutting back on the mediocre junk that floods the searches, and buyers will be thankful for it. I know that I'm happy to see this shift in the business.