I just remembered a way it is possible to corrupt a Mac HD with a windows virus--it is possible for those who dual boot OSX and Windows thanks to the Intel chip. A decent virus worth its salt doesn't care what files it attacks on a hard drive or what partition if it is downloaded through Windows it can and will infect whatever files it can get to and may just as likely corrupt Mac OS by corrupting the Hard drive itself when both OSes are present on a single drive--such a thing is not unheard of.
Boot Camp separates the two partitions in such a way that Windows can't even detect the OS X partition, which makes it safe from all current known attacks.
It's a good point though, if this changes, and Apple allows Windows to mount the OS X partition, then things start getting messy.