Well I think they're the same.
Button may have seen him coming for longer, but that doesn't mean he would expect to be run all the way off the road, why would he? He only realises that at the very end, and has to react quickly. Why he would he wait till he was on the grass to lift, if he knew what was happening earlier? Hamilton also had a small chance to react quickly, but legitimately tried to hold his road position, as Button could have elected to.
In my opinion, if Vettel and Button collide, and take out a few other cars, Vettel would have been penalised too, maybe with a ban. (He would also have won the title that weekend, though). Perhaps that makes it look worse in my eyes. Maybe Vettel isn't so cold and calculating as that incident, in that context (Button the only driver that was still mathematically in with a chance), makes him seem.