The high end laptops may allow you to upgrade video cards. I notice the Dell XPS laptops have the standard Geforce Go 6800 Ultra and the OPTION to upgrade to a Geforce Go 7800 GTX video card with PCI-express x16 interface. Hmmm. It's probably like changing the RAM on the laptop where you open the panel on the bottom to access the card or something like that.
Either that or they make laptops with separate integrated Geforce Go 6800 Ultra and 7800GTX cards.
they make seperate labtops with different cards thats all. you can really change it because if say some cards that normaly take two pci slots in a regular desktop cant be used in a labtop.