Canon's new Rebel T4i (a.k.a. EOS 650D) has a new "hybrid AF" mode, which allows continuous AF during video, but only when used with one of the new STM lenses.

I've seen chatter on the web forums where it's suggested that this is a greedy move from Canon in order to force people into buying new lenses. I understand that STM allows a better AF experience during video, but is there a technical reason an STM motor is a hard prerequisite?