For those of you who want some background on why big publishers have mostly abandoned the midlist, this article[1] by Kevin O'Donnell is a good summary. Short version: A Supreme Court ruling related to tax markdowns on slow-selling books made it too expensive for publishers to hold paper inventory of midlist books from year to year. On the other hand, since e-books don't create excess inventory, there are no tax penalties for Amazon (or Apple, or B&N, or whoever) to keep a midlist book "in print."

[1] http://www.sfwa.org/bulletin/articles/thor.htm