All the other people's habits stuff aside, in the world of mobile services unlimited was created in connection with there not being any overages or extra charges associated with it. Implications of some sort of speeds or anything like that were not in the scope of it all.
AT&T would have been better off keeping unlimited folks on to 3G and not letting them use LTE. When you get throttled they are supposedly throttling you back down to 3G speeds (UTMS supports up to 384kbps). At least then they wouldn't have to worry about throttling as it is pretty much too slow to use.
I switched off the unlimited plan cause I wanted to tether and was tired of having to JB my iPhone to do it. Plus I really don't use that much data in a month...