Anniversary Dance?

Can someone explain to me what the anniversary dance is and how it works?

I thought is had something to do with the couple that was married the longest or something.

They ask all the married couples to dance to a song. As time goes on they start kicking people off the dance floor by increments of years. For example, they say 'leave the dance floor if you were married today, leave the dance floor if you have been married 1 year, 5 years, etc. etc.' Then the last couple standing has been married the longest and usually the bride and groom acknowledge them.
Personally I don't really like this because the bride and groom get kicked off the dance floor within seconds, and it's their day!!