Sony's registered a patent for something known as degradeable demos.
It details how a taster could be the full game itself, with features and levels disappearing over time or depending how far you've got along with play.
A couple of examples given by SCEA, who registered the patent, shows how strong a weapon can be, before degrading over time to a weaker weapon.
Another one shows race tracks being removed one-by-one, depending on the progress made in the demo. Once you the full game, however, you can gain back whatever features that degraded in the taster.