The people who say the game is all luck and no skill are just using it as a cop out because THEY have no or little skill.
Like I said, I've won several games online. It's not simply about having the most speed, as that would be too easy. It is essentially an arcade racer, so you need to take into account the arcade elements like blue shells, stars, etc to strategize and win.
Besides, the longer you stay in first, the more likely you are to win anyway, because you tend to put more distance between yourself and the rest of the racers, as the people behind you all hit eachother with items while you are in the clear. Sure, you will probably get hit with a spike shell eventually, but if you are good enough, it usually shouldn't matter.