Well most peple won't think to look for a cracker AND if you password is say 12 chars long, they won't crack it without utilising hundreds of PCs in some kind of SETI screensaver type arangement.
I think you're seriously overestimating the time it takes to crack most peoples 12 character passwords. That is assuming a Brute Force attack is even the best attack strategy in the first place. Considering it's a Microsoft product, I can't imagine it not having one or more serious security vulnurabilities that open up for much more elegant attack strategies than simple brute force (I mean it is RC4 after all).