This is to stop pirating I'm sure. People have to actually buy the game god forbid >=O. I've heard that if you conect through a cord, or "link", with a friend then you end up playing online at the same speed as a lan. No harm done.
Last I read its confirmed there will be no LAN for SC2. The new battle net system must be fast or something...dont professional players play through LAN? I myself would much prefer a LAN connection when I play against someone in the same room that way I know the connect would be more reliable and better quality than online but we will see. Blizzard people are smart, I am pretty sure they know what they are doing.