story
1. Better choice of desktop environment (KDE/GNOME vs OS X)
2. Wider/better selection of applications
3. Better development environment
4. Ease of deployment of your own apps
5. Better fit for your budget (why spend 3000 Euros on a limited set of features, when you can spend the same amount and get huge number of features/better features)
6. Capability to connect upto 3 external displays (which Macbook has got only recently)