In the network ratings game, given the ESPN vision of tennis and the tennis fan, this is what is. They have apparently gauged the level of the audience, what US tennis-watchers want to see. Ratings boom, apparently, when Agassi, Williams or Roddick play. Blake also to some extent; he filled Grandstand 2 at IW for a second-round match.
They are not going to tell us that they are showing mediocre matches because it would be an admission of the fact that ratings and profits are the dominant factors in deciding match coverage. They are not going to because they are marketing a product. If they did, most of the lukewarm tennis fans would turn off. Perhaps a few more hardcore fans would tune in, though most of those already do.
I would guess they lose at least half their audience showing a tight contest between Schalken and Robredo, for instance. Of the half they lose, they might gain 10% back through additional hardline fans tuning in.