Chafic wroteA gaming mouse has more buttons and faster "click speed" . A gaming headset just gives you the surround and the main sounds of the game, whereas a normal good quality headset gives you a open sound instead of the details.
The 7.1 surround of gaming headsets is often accomplished by having multiple drivers inside each ear, giving a fake transition between channels and never sounding as good and natural as proper stereo headphones. Good quality headphones have better soundstage, and with a good game that supports stereo properly (BF3 and CoD are excellent examples), the amount of precision that you can get with good stereo headphones in terms of position is breathtaking (personal experience). For games that are not so good at positioning with stereo, you have virtual surround that can do the job pretty well, and a selection at that (Soundcards: Creative has SBX ProStudio, ASUS has Dolby Headphones, and Razer has the Razer Surround software that has recently had people dumping their soundcard virtual surround features in favor of this. Try it on your PC).
The detail resolution of good quality headphones is higher. You don't necessarily hear as much detail using gaming headsets vs. good quality headphones.