Because there is still some support needed for 64bit machines that not even windows 7 compatibility can fix. That's why software companies need to work on patches and not be lazy again.my college reccomends both pc or mac, they frown upon linux. i went and got me a uMBP 15" and i havent used a personal windows os since ive been at school. the pc labs now they have the software you need.
ps our school has some nice imacs but it makes me cry when they erase osx and put xp on it, wasted a good machine especially when they get win 7 free