Actually a great tool to monetize demos like Psn+. You like what you played? Press this button to unlock the full game! You've already downloaded it...why not? Smart idea. Not a new one but a smart one.
It's total shit imo (assuming it's like psn 1 hour demos)
You have to download the full frigging game just to try it out...
Who is going to waste their time downloading 10-40 GB for a demo (this is what MS/sony hope I guess, that you committed to so much bandwidth and time that you're inclined to buy it)
Giving you a savegame in a demo is not a frigging special or new feature, you can download the (long and great) demo of dawn of war 2, then if you buy the full game it'll update your install with the data of the full version and you keep your savegame.
I'm also 99.9 percent sure dragon's dogma demo lets you keep your savegame in the full game.
Other game demos have had savegames for ages , it's not rocket science... very very basic stuff.