Believe it or not, despite of the most generous time controls features here on BK, there are some people that systematically Time Forfeit their games.

I would be more interested in a TF(%) on someone's profile rather than a deceptive average speed.
When someone goes on vacation during the summer, this average speed may drop significantly without representing the actual playing speed of a person.

And, of course, Hrqls is right. Some people do take their games seriously enough to think more in one type of game(e.g. Grand Chess or Shogi) than in another (e.g. Dice Chess or Ludo)...