Interesting thread with some hilarious replies
As for my take on what a "non-game" is:
I don't agree with that a (video)game has a winning condition in the sense that you can finish the game with a victory screen. This would exclude what I call "endless" games such as Tetris, which seems silly.
I'd classify it a bit more as an activity requiring user interaction in order to achieve certain objectives by overcoming certain challenges (what the user does has a noticeable affect on the outcome).
* This excludes Visual Novels which only requires the user to press a button to watch the next bunch of text, but does include those Japanese "adventure" games where there are story branches to choose from. One objective in those games is "collect all the possible endings". Granted, it's not very deep gameplay.
* As for Tetris, the objective is to survive for as long as possible, and lower level objectives would be to clear lines.
* This includes Animal Crossing, The Sims, SimCity, Nintendogs and other "simulation" games as they do clearly have objectives/challenges. In Animal Crossing these objectives would be things like getting a rare fish for Tom Nook. In The Sims it would be to get your Sim a job promotion. The most fun in these games is usually derived from creativity in the ways of interaction. Note that a lot of these objectives are not mandatory in the game, and the player can even decide his/her own objectives.
* This excludes Mario Paint, the DS dictionary, and that Tarot cart for the NES. But does include the DS Brain Training game as it does seem to have challenges the player must overcome in order to proceed (correct me if I'm wrong here).
None of this really matters though. If people want it, they'll buy it. And there will still be "games" out there for you, whatever your definition is.