After all that's the way Adblock Plus makes most of its money, needed to develop the browser extension, port it to new platforms, maintaining and hosting the filter lists (which by the way are also used by every other ad blocker). I doubt that if Adblock Plus wouldn't have done this step, it would have ever been ported to other browsers and platforms, and that the filter lists (as mentioned, also used by other ad blockers, like AdBlock), would have been that well curated as of today.

So I don't see anything wrong with that. Or does anybody complain, that most free Android apps show adds, and you have to buy the paid version, to get rid of them? No, everybody understands that this is the way they make money. The only difference in case of Adblock Plus is, that you don't actually have to give them money, but just have to disable a checkbox in the options.