Hell, I think you're both right. I wouldn't call it fun, I'd call it enjoyment. Fun Factor would be instant enjoyment, and Motovation would the anticipation of future enjoyment.
Yet another example: World of Warcraft. You can't argue the success of this game by any means, and...let's face it...a lot of the game isn't all that fun. It isn't fun to shoot your 3,000th shadowbolt at the 428th level 2 zombie that you're killing for the night. But there's motivation in it. Level up, see the "cool" stuff in the game, and experience fun at THAT point with your friends. Motivation STILL persists here, though, to either get better and better gear, or to pvp with other players for various rewards. Overall, though, a good chunk of the game isn't directly fun.
See, the player belives that when s/he gets teh rewards s/he will enjoy the game more, or simply be happy to have it. They are motivated by the anticipation of future enjoyment.