Maybe different Google departments have different opinions about such things. Chrome's error pages include a game http://www.omgchrome.com/chrome-easter-egg-trex-game-offline

But performance-wise, the error pages still load instantly and don't waste CPU when the game isn't activated, so who cares?

...though I don't know why anyone would care about slow 404 pages either, given that they should be rarely visited and quickly left.