Using GLUE on consumer electronics, in fact, on an item which will get hot during use and break down the glue over time, is crap and badly thought out..
I see peoples screens falling out of these iMacs after they have been used for a year and half, and your only option will be to re-glue.
Magnets would have been, and have already been used as, a more intelligent, inherently superior solution, glue is just cost cutting to up the profit margin.
Screws would have been an inherently superior choice over GLUE... glue is NEVER the best option, glue degrades over time with environmental factors, screws do not.
So where do you suggest they screw the screen into? Logic tells you that if you want the glass/LCD to be a single unit, and the rear housing to be unibody, there can be no screws.
Apple have ALWAYS put design over practicality - if you see one of the new iMacs in the flesh, the first thing you'll say is "Wow that's thin". Nevermind that it's not much thinner in the middle than the old one, and the footprint is the same - it looks striking, that's what Apple have always done (and quite frankly, what they do best).
The % of people who open the iMacs is incredibly small - and to be honest, I'd rather have to heat some glue, than have to spend an hour removing dust from between the LCD and glass. Same goes for the VESA mount - in ~ 2 years servicing iMacs - I've seen one person who has it mounted - myself.