I just upgraded from a 16mp D7000 to a 24mp D7100 so I was a bit disappointed to read this thread.
I decided to do a test and resubmitted a picture taken at 24mp which was rejected for focus issues. After downsizing, it was accepted in Shutterstock. (I also did some reprocessing of colors and cropping, but that was not the issue for refusal)
The original picture accepted at fotolia but not at SS
http://www.fotolia.com/id/64257005
and the picture accepted at SS after downsizing
http://www.shutterstock.com/pic.mhtml?id=189941966
I will do some more test in future with rejected pictures for focus issues.
I decided to do a test and resubmitted a picture taken at 24mp which was rejected for focus issues. After downsizing, it was accepted in Shutterstock. (I also did some reprocessing of colors and cropping, but that was not the issue for refusal)
The original picture accepted at fotolia but not at SS
http://www.fotolia.com/id/64257005
and the picture accepted at SS after downsizing
http://www.shutterstock.com/pic.mhtml?id=189941966
I will do some more test in future with rejected pictures for focus issues.

