Yeah, I'd say it was the Indiana Jones thing primarily. Not too many actors have that cred for being associated with the action/adventure genre that Uncharted fits under. Plus, it's always novel to see the older generation get into games but his reactions seems somewhat genuine (OK, so he's a good actor as well).
The brief glances alone were enough for me to agree with his final statement. Incredible. I'm just hoping I can get through Batman before it comes out!