Call me a cynic, but I think some architects build elevated back tees to placate their most important critics - the top players, the raters, the writers, etc. - who will likely be playing from back there. These golfers then won't complain about not being able to see everything, plus they get at least a psychological boost on their drives, if not so much of an actual one. (Aside: I can't believe Jeff's numbers are correct, 1:1 sounds way too little to me).
I personally hate elevated tees - yep, hate them. And not just because of my fear of heights. They look unnatural, they remove an interesting element of the game (visual uncertainty), they help out the wrong golfers, blah blah blah. I also think they are a big part of why people rate canyon courses - at least the few I've played - so highly. Perch the big boy on a cliff, and let him bask in the glow of his power. Yuck.
AG -
I could be wrong, but I would think elevation affects longer clubs more than shorter clubs. This is judging by my own (limited) experience, as well as the fact that the shorter club's shot is likely descending on a steeper trajectory. Draw a couple parabolas on a piece of paper with different relative steepness and you'll see what I mean.