Lucky them that Napoli was dropping points already or otherwise they would be miles behind in the table despite not losing any games. Next stop is Aston Villa for them and it is probably not going to be another draw without goals.
Yes, the gap between Milan and Juventus is quite a lot from the teams at the top. It's just that for Serie A, the competition is very tight. In fact, the points of the clubs from top 1 to 5 are only 1 point different and even exactly the same. So every match in Serie A is very influential on their next position. They must be much more vigilant with this one condition.
Source: Serie A table
Yes AC Milan so far is the biggest loser I think. They aren't any worse than the other leading teams on paper in my opinion, but well, on paper is worth nothing if they can't bring it into the game. But their performances is so volatile. They beat Real Madrid in the Bernabeu stadium and fall so far behind in the domestic league. But the funny thing is that they dropped points against teams like Cagliari and Parma. Atalanta is taking place very soon, which could very well end in another setback for them. They could be like 15 points behind the top in just a couple of weeks from now and then the season essentially has barely any value for them. It would be a lot about making it not look too worse.