why do they tell us pro athletes' salaries?

[astro]

Name the people who would benefit for keeping athletes salaries secret.

The owner (maybe)
Name the people who would benefit by the info being available.

Player - negotiating strength as salary sets marker
Union (by extension) - open salary info encourages fair negotiation
Players representative/lawyer - a big salary is huge feather in his cap as a negotiator

[Donnerwetter]

@Lukeinva

When Jaromir Jagr [ahem] played for the Washington Capitals I was really entertained to learn his bi-weekly paycheck was $900,000.

There you go. You are certainly emotionally involved because you are privy to that information and likely to follow the games.