I guess form factor could be a major part of it, although the 15" MBP does support DVI. And there are lots of laptops with decent non-integrated video cards but

I guess form factor could be a major part of it, although the 15" MBP does support DVI. And there are lots of laptops with decent non-integrated video cards but no DVI support -- support for DVI isn't exactly a high-end video card feature, after al.