How much genetic difference is enough? It is obvious that there is a grouping of features beyond skin color. Where you put the line between races is somewhat arbitrary - and this is the same with all concepts, so it doesn't make sense to think about genetic difference (e.g. in Rwanda Hutu and Tutsi are considered different races, even though genetic difference is almost inexistent http://en.wikipedia.org/wiki/Origins_of_Tutsi_and_Hutu). People have established this concepts because they are/were useful, and will continue to use them.
Furthermore the name was created on fallacious premises to begin with. From the creator of the "Caucasian race" Johann Friedrich Blumenbach:
Caucasian variety - I have taken the name of this variety from Mount Caucasus, both because its neighborhood, and especially its southern slope, produces the most beautiful race of men, I mean the Georgian; and because all physiological reasons converge to this, that in that region, if anywhere, it seems we ought with the greatest probability to place the autochthones (birth place) of mankind.