Depends on who they're playing. When they play another small market team, yeah, the ratings are bad. When they played the Knicks (1999), their ratings were almost twice what they were versus the Cavs. So it depends on the matchup.
Meh; that doesn't speak to the fact that the Spurs are one of the least popular teams in the NBA, and there's no reason for Stern to want to cheat them into the Finals every year, especially if that means that the fan-friendly Suns can't go.
And Cleveland may be a small market team, but they have one of the biggest sports stars in the world on their team, and that wasn't enough to not have the lowest rated Finals in history.