Could be as simple as not counting floors or providing less points for excessive time spent/bonus points for being quick. But the exact details would naturally be up to Blizzard.
Either way, this is by it's very nature something that would only affect those competing for the top, since you're hardly going to care if you're place 50,000 or 50,001. Anybody who doesn't care for the competition is free to spend as much time as they feel like. Power rewards are supposed to bottom out fairly early on either way, so they're not a significant concern.
Then go elsewhere. This is a bit like complaining about pet battles.