Anybody know, what is difference about game:

Syberia The World Before
and
Syberia The World Before Prologue

The Prologue is a demo.

But download is stil 2,8GB. Why 2,8GB just for a demo?

While you can download the prologue here I would suggest you get it from Steam. They released a patch there, adding 6 new languages, bugfixes, improvements and achievements. If they don't care to maintain their demo, how much worse will they treat us when the final is out in March? How long will we have to wait for updates? A clear sign to stay a far ways away from this one.

Depending on how it's built, it may be easier to impose various artificial limitations on the full game rather than chop the full game into tiny pieces.

You all say it's a demo, yet I have both a Demo AND the Prologue, along with the game itself in my library. That's right, all 3. The Demo is also nearly double in size, compared to the Prologue.

Are you sure it's actually a demo and not a small stand-alone "prequel"?

I don't know for sure given that I haven't played it, but "Prologues" are usually short games with a story set just prior to the main game. They are released for demo reasons though as they introduce the mechanics of the game and give you a taste of the world - a demo without actually being a demo.

It's a newer tactic to get people hooked into buying the full game is all. It's a little strange they released both a prequel AND a regular demo, but I guess the devs cast a wide net to pull in as customers as possible and tried both tactics.