yes it is just for fserves, believe it or not. (I know, it seems too crappy to believe, but believe it)
Try setting it to a number lower than you know your available bandwidth and DCC a file to someone. It will go higher than what is set there.
Now setup an fserve and have someone get a file from it. It will follow the speed limit.
Since I've used the fserve part of mIRC quite a lot, I know all about this, and it is extremely annoying