If you sell fifty thousand copies for fifty bucks after a two million dollar development cycle, you just busted your balls big time at retail. When you sell fifty thousand copies at 6 bucks for a game that already made it's money 15 years ago, that's a solid three hundred grand and little to no costs to get it ready, with the cost of putting it out for dissemination being a small fraction of the return.
If you sell 50,000 copies for $50 and your cut as an online store is 30% (which seems to be the norm), you made quite a lot of money as an online store ($750,000). If you sell 50,000 copies at $6 with the same cut, you made a much smaller amount of money ($90,000).
When the game made it's money isn't relevant since we're talking about the online store and not the developer/publisher.
