Too late, I got it a few weeks ago, needed it then. I went with the 2TB option.
I can either add one after market or sell this one when the new ones are in.
I'm assuming simply because you can more cheaply have the 256+1TB HDD, which, if you know where to put things, is just as fast with 2.5x the storage. They offer the larger drive on the MBP, as it "officially" has only one bay for a storage drive.