why would apple need to drop the 15" inch monitor since it is almost the equivalent of a 17" inch crt which views 15.5 to 16 inches and is plenty for the average user?
there is nothing wrong with lcd screens ranging from fifteen to twenty-two inches and also a consumer level lcd imac on the market with a 15" or even 14" inch lcd since the viewing area now is 13.9" inch viewing area on the current crt model
I think the average computer user opts for a 15" screen if they do not know any better. It's definitely cheaper than a 17" or up. Just like jefhatfield said, the actual viewing areas are so close with a 15" LCD vs. 17" CRT that it wouldn't make much sense to get rid of it completely. If Apple did this, then I would imagine they would sell less displays since a 17" costs more than a 15"....enough to warrant purchasing possible other hardware...