What on earth..?
The MacBook Air is an ultra portable laptop. Make it a 15" and you are carrying a big foot print but really underpowered for what you could get for a little bit more thickness of the 15" MBP.
It isn't a "why would anyone want an LCD screen" question, don't know what your smoking to think that is relevant, it just is pointless.
Make it 15" and it isn't an ultra portable laptop.
Thin isn't that good a thing..
Back when the CRT was king, people could not understand why I spent $400 on a 15" LCD. There were many techies who insisted that LCD's had inferior picture quality, too expensive, and so on. Now look where we are. Maybe you are too young to remember, or too young to understand my point. Basically, don't dismiss anything that you can't easily wrap your mind around.