I don't have to prove you with the link, think about it.. those are all the facts I read off the web and from my friends that know more. 
64 bit has a 64 bit wide path...which lets data to excute faster than the 32 bit wide path, similar concept to driving on a 2x2(4) lane freeway vs a 4x4(8) lane highway.
Games today are not optimized to run on 64 bit probably because of the video card isn't supported for 64 bit and the application itself.
The application Mathemetica for Mac OS X written for 64 bit is faster than the 32 bit version.
