In Drogba's case, I'm guessing they felt that punishing him for his treatment of the ref was punishment enough. But had he only yelled what he did into the camera and not spoken to the ref, I'd hope he would have been given a 3-5 match ban.
As far as yelling stuff at refs go, it's completely different. When a player swears at a ref, we don't know about it. When a player swears at a camera, you're broadcasting swearing to millions of people. It's a completely different situation. Not only that, it's completely needless. I can understand a player swearing at a ref, but swearing at the camera? There's no reason for it, which is why it never happens. Now as far as players abusing a ref, I do think they should be punished more harshly, but again, bringing up lenient decisions in completely different matters is off-topic, and as I said before you can't use it to prove bias against any particular club. The reason it's more difficult to punish players for swearing at refs, and sometimes they get off. For example, sometimes you can't prove whether or not the player swore at a ref. If he yells "****!" when the whistle is blown, you don't know if he's swearing at the ref, at himself, or at the world in general. Maybe it's obvious that he's swearing at the ref, but the player could always claim that he was swearing at himself for committing a stupid foul. Also, there's the question of language. A player may easily insult a ref in a different language without the ref knowing, and then you could cite this lack of punishment as inconsistency. But I'm getting way off-topic. Dealing with refs is a completely different type of incident, and one that is much more difficult to punish. This incident is pretty much without precedent (why they had to make an example of him) and is very easy to punish.