I honestly don't know why you would need it, it works fine on mine and I'm on 64 bit windows...
Have you tried reinstalling the game? all I can think of is something went wrong with the download procedure, unless of course the game relies on some Net Framework that a user needs installed on, but usually a game that does would warn the user...
Another reason could possibly be there is some incompatibilities with a fresh install that people who already installed the game before a certain update don't get, one of us would probably have to reinstall windows to test that theory though... xD