But that's not taking into account the replayability factor. Rush of Blood may take less than two hours for a first play through of each level - but that's not including alternate routes, finding all of the collectibles and aiming for a top place on the online leaderboard.
You said you're not interested in leaderboards but others are, which will increase the games longevity. Those games may have only lasted you that amount of time, but that's not an indication of how long they'll last others.
Another thing is VR's social aspect. I never thought it would be such a great piece of hardware to play with a group of friends - it seems like such a solitary device. But I can't even count the amount of hours I've had friends over and we've all taken turns to play single-player games, including VR Worlds, and had a go a Playroom multiplayer.
Do you count these hours? I may not have been playing all that time but I've still been enjoying the hardware and experience with my friends.