I cannot think of what a desktop can do and a laptop cannot. I do not see the necessity of using a big heavy duty desktop nowaday. I will not buy any more desktops. Laptop is also going to be phased out in my family. Netbook is what I am doing for its size and $
a) a midrange desktop gives you far better performance for the same $$$.
b) laptops will always be short on high-end performance due to heat dissipation issues
c) the small, low consumption budget conscious desktop is called the nettop, but these have not had the time to become mainstream yet
d) as for extendability, while you can go the usb route, it's more expensive and leaves you with a forest of cables.
