I think there is also the F**k You factor that the GB&I team has that we don't. Paul Casey said it several years ago when he stated that they bloody hate the U.S. team when it comes to the Ryder Cup (I'm paraphrasing here). He took a lot of grief for that comment, but I think it's very true. They have the attitude towards the guys on the U.S. team that they are prima donnas, we're arrogant about our world rankings and that we play on the best tour in the world, so how can we lose. The U.S. doesn't have that attitude toward GB&I. I don't see any dislike for them when it comes to playing the Ryder Cup matches, until Patrick Reed came along this year. They might not admit it, but I think they still have some of that dislike (F.U. factor) towards us and it fuels their fire.
I think that's why the U.S. performs so much better in the President's Cup. The International team doesn't seem that have that dislike for us the way the GB&I team does. When I watch those matches, it appears to be a much more cordial event and the U.S. team seems to play their best.
I know captains play a big role, but there are so many other factors at play. JMO.
I think this observation rings true.
The list of U.S. Ryder Cup players (since the inclusion of continental European players in 1979) who have won a major and have losing records in the Ryder Cup is pretty lengthy: Furyk, Bubba Watson, Webb Simpson, O'Meara, Love, Leonard, Crenshaw, Couples, Duval, Bill Rogers (!), Payne Stewart, Strange, Toms, and led of course by America's best two golfers the last two decades -- Mickelson and Woods. It's far longer than the list of American major winners who have winning records in the Ryder Cup since Euro' 79: Kite, Pavin, Wadkins, and Irwin sort of (he played 3 of his 5 RCups from '79 on).
The list of Euro players who did not/have yet to win a major and have winning Ryder Cup records is lengthy as well. Players of fairly modest accomplishment who never won a major -- Parnevik, Casey, Rocca, Pinero, Canizares -- all have winning RC records since 1979. And then there are the big ones; none have won a major, and here's what they've done in the Ryder Cup:
Monty: 20-9-7
Garcia: 18-9-5
Westwood: 18-13-6
Poulter: 12-4-2
Donald: 10-4-1
I don't know how you compare those two lists and not come to the conclusion that European players simply take the Ryder Cup more seriously than U.S. ones do, prepare for it better, and perform under the pressure of the Ryder Cup better than the Americans. Euro is simply better at this than the U.S.