I do agree with you to som degree about useless functions, but this function is very usefull and should be avaliable on a pro camera without the need of accessories. I use a 550D, and this function is great for group photos. (I even have Auto ISO in M - mode).
I have never used the 5D3 (nor the 5D2), I´m gonna upgrade my 550D in a year or so, spending my cash on lenses first and foremost, but it is surprising that my little consumer camera has basic functionallity these pro bodies does not have.
(Perhaps a low blow, but it is worth mentioning, Canon is also selling themself as a environmentally friendly company, and having to buy hardware to get basic, software functions is everything but. That is just being cynical )