I fail to see how Westbrook is any significant upgrade from Henry. Even though the Eagles clearly have a better offense, they don't line up with 2 TEs and run Westbrook, even at the goalline. At least with Henry, you know he's going to get 20+ carries every week, and I gotta believe at some point the offense will improve.
Additionally, Henry already had a BYE (but not the Eagles), so there's another week you'll be with only 1 RB.
While I like Hasselbeck, to give up Manning for an exchange of Westbrook for Henry is piss poor IMO.