well if he won, he would have crossed the line and finished the race. and yes, he would get a 10-place penalty in the next race if he changed his engine prematurely. silly rule but that's the way it is...
Now I think Honda should've let Button take the points and the penalty, maybe next race he won't even finish. And is Button bad at catching up with competitors? He seems to qualify well and then try to not fall back too much.