Like all things digital, the 2.4GHz systems are much more complex than old-fashioned analog, and thus require processing time, mainly when converting digital signals to analog waves and back.
Although minimal (calculated in the milliseconds) this still adds a delay to the controller's signals, and while the general population racing RC cars may not notice or care, the upper tier rely on precise movement and split-second timing when controlling their car, and do notice anything that is off from their well-rehearsed routine. Often they'll find they're going wide on every corner because in their minds, when they move the wheel at this precise spot, the car should react accordingly. Even 3-4 milliseconds can throw this off, especially dealing with speeds in Mod.
If you're concerned about the delay in a 2.4GHz system, just switch to a servo that's .01s faster than your current one. the .01s difference of a faster servo will more than offset the .003s delay.
I think "Faster" is a relative term when it comes to 2.4GHz systems.. The newer ones (DSSS, FASST and Spektrum Pro) are "Faster" than the original Spektrum system, but are still calculating time in terms of "added delay" to an analog radio.
I've never tried Spektrum or any 2.4GHz system myself, but I don't think I will be doing so anytime soon. Not that I'm good enough to notice a few milliseconds added to my reaction time, but since everyone else around me seems to be switching over (at least 50-60%), it leaves me with a lot more choices of frequencies on my 75MHz band!
