It was just one whale buying everything, there's a fine medium somewhere. People looked at those sales and thought that was the basis of all collectors... it's not, it's just one rich guy and his money.
Say a title goes for about $150 sealed on average then someone gets a VGA 90 of it. So they're probably $200 into it themselves. There will be plenty of buyers at the $300 / $400 / $500 level based on the premium grade. The problem is that this title was selling for like $10,000 if the whale needed it, so ignorant buyers assume that's the value on a VGA 90. Yet the real value may have been closer to $1,000, but the market never got to see it.
So prices are still moving up in a steady fashion in you really know the fair value of an item. You just exclude those outlier flukes and sealed games are as healthy as ever.