The thicker books do tend to be older material, and I'm all for that as these are the only Premiere format books I now buy. It's the "ongoing" Premieres (if that makes sense) that seem to be shrinking. Of course it's not all of them but, looking through the Spring 2010 release list that was linked in another thread, more and more of them are getting smaller.

Fortunately for me, most of the books I'm interested in are getting the oversized treatment in one way or another so I'll stick it out and wait for those.