The client people are downloading is different from the old one. In fact if you have the old one installed it will delete the old GW2.dat and redownload everything (and update the downloader along the way).
The download rate showing on the downloader is also incorrect, it's actually download at 3-4x the rate showing and is pretty much running at max speed on my connection, very fast indeed.
Also from what I've read the total client is around 12.7 gb so an extra gb over the old client.