My understanding wast the reprint editions, (the Collected Jack Kirby Collectors) would stay the same size as they have been in the past, so they would still sit uniformly on bookshelves.
The other thing that occurred to me was that the email did mention color. Some of the other Two-Morrows magazines that were regular size, (Alter Ego and Backissue), that were on regular non-glossy stock, and saddle stitched, switched to glossy, perfect bound, color, formats. Probably for the price breaks. I hope that's all it is.