Not really. The analogy would be:
I drive my car to the Mall and buy, say, a Playstation 3. After a while, I decide that I want more content to use on the PS3. Say, I want a new game. All that Apple is saying is that if the game is available to be bought OUTSIDE the Mall store, it should be available to be bought INSIDE the Mall store. Simple. Apple is not DEMANDING 30% of everything, it's just making sure that, once again, the experience is right. If Apple doesn't do that, probably all sorts of subscriptions/selling methods will pop and that will lessen the user end experience. The other thing is, if they allow to be only off-iTunes purchase, I, as a user, will have to enter my credit card info into dozens of websites, and be more vunerable. I'd much rather do everything at the iTunes store, with one password/one login/no hassle.
If Apple doesn't have that restriction (if it's available off-iTunes it should be available at iTunes, most companies will try to do everything off-iTunes just so that they don't have to pay Apple anything, and that will make the user end experience much less pleasant. Apple worries about that, most other companies don't.