Just read a great piece by Marion Zimmer Bradley about why stories get rejected. The key piece of advice is:
EDITORS DO NOT BUY STORIES BECAUSE THEY ARE WELL WRITTEN
The piece then goes on to list the myriad reasons why editors do buy stories and the even larger number of reasons that they won’t.
It’s nothing I haven’t heard before, but its put in a very succinct way that I think is worth a read for any aspiring writer:
http://www.mzbworks.com/why.htm
M Blackburn: A Writer's Journey 
I think that for the reasons that Marion Zimmer Bradley gives are why self-publishing is a very viable choice for writers these days. it puts the interest in the hands of the reader. Readers get to say what they want to buy and read, not just publishers.
Yeah, very good point. And maybe it explains why so much genre fiction is so ‘samey’… not only is it reliable for the editor/publisher, it’s also them simply promoting their own tastes…over and over and over.