@JBrunner: No, i think it gets worse for every day. The images has to stand out in an remarkable way picture-wise to have a chance of getting over their threshold to reject them on technical grounds. Though i have managed to get one very grainy 35mm Tri-X approved (even square cropped) despite that this agency is much more picky than Dreamstime or Shutterstock, and that shot was all about motion blur, murky shadows and reflections. I guess we could compare it backwards to a sport with umpire(?)/referee/scores, like skijumping. I remember when the swede Jan Boklöv started with his V-style. He had to jump very much longer than the rest to even have a chance to win.
For the customer it does not matter in most cases since actual use most of the time is web or quite small ads in newspapers and magazines. A good scan of a good 35mm shot is even enough for a cover of a glossy magazine, the paper and the print is also very good at smothing out grain in a very natural way. But i guess the inflow of images are so great that they many times take the easy way. I guess your advice to resubmit and hope for another reviewer is a good advice, at least for the bigger ones that have a team of reviewers.