I don't know too many people who are willing to give away a 12-hour game for free.

Maybe he said this because the single-player version of the game is estimated to take 13-14 hours to complete if you really stretch it?...;) I sure hope not.

IIRC, all of the Far Cry games save automatically at checkpoints, so they could easily create a demo in which all saves except checkpoint saves were disabled, and then end the demo, say, at the third checkpoint. No need at all for something as complex as "invisible walls." Additionally, to make the demo fairly small and lightweight compared to the shipping game they could remove the highest-resolution textures and disable the highest resolution display modes.

Demos are nothing more than a developer advertising and promoting the products it has for sale. Sad to say, but sometimes companies don't want to release demos because they are afraid that potential customers won't like it and will then pass on the game. In other words, the developer himself thinks the game sucks and doesn't want people to discover it until after they've bought it...;) Pretty sad. In this case I think the developer should worry less about "giving something away" and worry a lot more about trying to *sell* the game, instead.