Good point. It's definitely the same actor and what not, and he's obviously called Ghost for a reason, it could be that they still wanted him to be in MW2 but couldn't have Gaz for the above reason.
When Sheppard shoots Roach, I was so hoping that Ghost did actually manage to shoot Sheppard, but alas not.

I was so gutted at that point, but I vowed revenge and boy was it sweet. The fight between Price and Sheppard at the end was oh so epic, I was literally shouting at the screen "GO ON, GO ON PRICE! GET HIM!!1" and was screaming when Sheppard had him pinned, and the suspense of pulling the knife out and throwing it at Sheppard... My action key got owned on that part, but the bit where Price wakes up I just shouted "YYYYYEEEEEEEEESSSSSSSSSSSSSS!!1!1!!11"
Oh so so epic.