What I failed to think of until now is the percentage of fans who might buy tickets but not show up to the game. I'm sure the Indians track the "no show" rate but those numbers are obviously not publicly available.
Let's say that attendance is announced at 15,000 for a weekday night game against Kansas City. That same night, the Cavs are playing at home in the playoffs.
I wonder how many of those 15,000 tickets were advance sales or season tickets sales and the number of people holding those tickets that didn't show up.
Take the other night for example, when the Cavs were squaring off against the Pistons in game two while across the way the Tribe were taking on the Royals. Announced attendance for the Tribe: 11,048. If you read any accounts of the game, you know there were probably less than 5,000 people actually in the seats.
That number — the percentage of ticketholders who actually go through the turnstile — is vitally important to the club since those asses in the seats provide the most monetary value not by purchasing a ticket but by buying hot dogs and pop and beer once they're there.
The NBA playoff schedule isn't set in stone and is rarely known until just before a series starts. Indians tickets are usually bought well before that, and it doesn't take half a thought to not use them if there's something better going on.