James Mason, I dont know about lol DOTA or LoL (I played only cs go and Id never say that fast pressing was important there), but if there is one game that for me required speed is starcraft broodwar and starcraft 2.
In those games, I can feel the difference from a PS/2 connector and a USB one, and in case its not something you have had some experience with, usually is a difference of 4-25 ms that actually is a problem for me, as keys pressed on the keyboard and mice are recorded in incorrect order by the PC (usually at around 500-700 actions per minute speeds its something rather common).
However, only PS/2 fixes this, no USB keyboard can so far, same goes for mice, but I doubt more than 500 people on the planet run into this problem, so Id assume its not something that bothers most ppl.