Nobody can actually make money doing this unless they've already decided that what they're doing is going to be outright fly-by-night theft.
Bullshit! Mtgox was never designed to be a fly by night and Mark didn't actually profit from the exchange, it's ruined him.
Think about it.
If an exchange is not profitable and they have to choose between closing the business, or "borrowing" some of the bitcoins temporarily until they make up the difference next year, which do you think they'll choose?
The exchange will always choose the ladder.
It would actually make sense for the most successful exchange to be skimming the top, as that would give it the financial strength to out compete the other exchanges. Lance Armstrong anyone.