WTF is grup and why wouldnt the gameplay be the same.
GURPS, is the Generic, Universal, Role Playing System. Its a pen and paper based role playing game system that fallout was originally intended to use, however the reasons why it changed over to special remain disputed (SJ Games, owner of GURPS, say interplay dropped it without talking to them, Interplay say SJ games got squeamish over various things in the game).
For the most part, the game would play more or less the same. Click to shoot, move, reload, etc; but the back end on how the game works out if you hit/miss or pass/fail skill check was different, as is leveling and progression.
I've not played the demo, so I'm not sure which it uses.