Couple things, in order:
Remender books often have extra pages of story at no extra cost, and I think that's great. I never notice they're extra long until the letter column into, because he's just using the amount of pages the story needs. So, again, I don't mind paying a little more for those books.
I don't know a single publisher that divulges those numbers, let alone even talk about the 'why' except the occasional 'printing' explanation. Sadly.
Casanova got flack from retailers for being $2 back when it was an Image 'slimline book'. They didn't want to waste shelf space on a cheap book. So that might very well be a real concern at this point. Especially for Image, when a lot of shops still trade heavily, if not almost exclusively in Marvel/DC.