That would be a good explanation if they didn't make a non glass version that had the same wireless charging and signal as the glass versions. The problem is they do make a non glass phone with those things.Wireless charging and signal is what I'm going with (like others have mentioned). Rumor has it that Apple will go back to glass so they can get in the wireless charging game.
I think Apple's just trying to keep up with Samsung at this point. They've got to know people are getting bored of the same design and os. Them going glass, seems to me, more of a design upgrade than anything functional.