Not really the same thing. What you are talking about is loading an area before you get to it. Games have been doing that since the original Playstation, or ealier. But to play the games you mention, you still need to download them in thier entirety first, and then install them.
Last time I played Guild Wars I downloaded a 50 kb executable and streamed content as I entered new areas. Makes me wonder if you've even tried the game.
"How many teamsters does it take to screw in a light bulb?" "FIFTEEN!! YOU GOT A PROBLEM WITH THAT?"