When the benefits you gain from not logging in for 24 hours outweigh the benefits you gain from playing for 2 hours, I'll agree that we're being rewarded for not playing the game. As it is, this is just a small gimme.
You have to be logged off for a full 24 hours to get half a bar of 'free' XP. (One bar of double XP split between 'normal' XP and 'free' XP.) This is just not a big thing.