Gosh. Sounds from the description like you watched it anyway. Guess what -- so did tons of viewers who wouldn't have given two ####s if it had been Tommy Robredo on TV.
Tennis fans will watch no matter what. Joe Sixpack will watch only if it's the American stars. Tennis doesn't have strong enough appeal to sell on its own merits. ESPN would have to be run by monkeys to be stupid enough to put on anybody but Andre, Andy, and the Williams sisters, so long as they haven't been eliminated.
When you own a sports network, you can show whatever matches you please. At which time, of course, you'd show nothing but the American stars, because that's what sells, and you'd be in it to make a profit, too.
At this point in time, we should thank ESPN for showing the same mass-appeal types over and over. Tennis is on life-support anyway. If they started showing Argentinians, the ratings would die, and the next tennis event wouldn't be able to give advertising space away. Televised tennis outside of the slams would become a thing of the past. Better less than ideal tennis than no tennis at all. And that's the alternative, even though people don't seem to realize it.