There are more non-yankee fans than Yankee fans, yes, but the percentage of Yankee fans is greater than any of the other percentages. Ranger fans aren't going to watch Stras vs. the Astros. Neither are the A's fans or Mariners fans or Marlins or Cardinal fans. Fans watch by and large their team only except in extreme cases like the playoffs or the World Series or ASG or something like that. They know that if they want to maximize their viewrship the best way to do that is to include teams that have the biggest fan bases most often. That's why the Nats are on national games vs. the Phillies and Braves, two teams with wide recognition and fanbases. Now, when you can get Strasburg vs. the Yankees, like is projected to happen on June 17, then you've got something, but Strasburg alone isn't enough of a draw to turn the ESPN cameras, no single pitcher is.
Gotta disagree again. I can't imagine Rangers, A's, Mariners, Cardinals et al fans, the vast majority have seen Strasburg pitch once (his debut) would not want to see him again as opposed to seeing yet another Yankees game (remember they were on last night) against the Twins. And I'm even more confident that other NL East fans (and probably Orioles fans) would rather watch Strasburg, in the hope that he fails.
And he's not just another good pitcher because you see other good pitchers on national television. You never see Strasburg on national television. Again, I'm sure most baseball fans have seen him pitch once, twice at the most and haven't seen him at all in almost two years. That's not true with any other "really good pitcher".
Remember this isn't a game between the Yankees and Red Sox in September. This is a Yankees-Twins game in April! Freddy Garcia vs. Carl Pavano in APRIL or the most hyped prospect ever who you've seen once (or twice).