Google's point here is to obviously make them as invisible as possible to minimize users that block ads. Most people won't go around other android stores or internet sites searching for software, they're fairly happy with google play.
Quite right! Until today, I didn't know that there were ad blockers for Android. With today's action, not only has Google made me aware that there are, but, thanks to TFA, I know where to find them: F-Droid. Excellent!!