That seems strange to me. 15" seems like a pretty standard size for carrying cases, etc. 17" made sense as significantly larger. Unless they plan to replace the 15" with the 16" and get it in the same chassis form factor, this seems like overloading that space with too many options. Apple generally has pretty segmented product lines, perhaps one good option for large categories (casual users, power users, etc.) without making you think too hard after getting in a general segment.