It is surely true, that there are different types of gamers. The ones who need long long gameplay, who want to dive in another world for months. And the ones who need some action or fun for only an hour a day.

But thats not what sells games.

IMHO, the only thing what sells games is it's popularity and how it got review by e.g. game magazines, tv shows (giga tv in germany for example). If the media says it's a good game, then people buy it. You can make one of the best games, if no one knows it, no one buys it.

So our all biggest problem is publishing, advertising etc.

I think to start with adding a demo on a game magazine CD is a good thing. But also there it depends on how you do it. If you provide a demo with just the first level, which is boring because your first level is just made to get the player familiar with the controls then you already lost. A demo of a game should only have one goal. Convince the player on the one hand that your game is full of story and has deep gameplay, or on the other hand, that your game is exact the right thing for him to relax by having some action or addictive puzzle time.
It doesn't matter if graphics and sound are the very best and absolutely up to date. It must fit to your game and must provide a consistance in style so that the game looks like a well finished and polished piece.