Considering how lopside the matches where and how early the coverage came on in the Western U.S. (it does exist!), these ratings don't seem that bad. From Larry Stewart in the L.A. Times:
NBC might be doing well with football on Sunday nights, but it did not do well with the Ryder Cup. With European golfers dominating Americans over the weekend, those ratings were down. NBC averaged an overnight national rating of 3.0 for its two days of coverage. In 2004, NBC averaged a 3.4 overnight rating. Final national ratings were not available.
In L.A., the Ryder Cup got a 3.0 rating for Saturday's coverage and a 2.1 for Sunday's.