According to a story at Android Police, a number of developers of Android apps which have the capability to block ads in Web browsers have received notifications from Google that their apps have been kicked out of the Google Play store and are no longer available for download.
The notifications from Google clearly note that the reason the apps are being pulled is because they violate the Google Play Store's developer agreement:
REASON FOR REMOVAL: Violation of section 4.4 of the Developer Distribution Agreement.
After a regular review we have determined that your app interferes with or accesses another service or product in an unauthorized manner. This violates the provision of your agreement with Google referred to above.
A search for "adblock" on the play store this morning returned no relevant results, and directly accessing a URL for an ad-blocking package shows the package's page and a notice that the app is "no longer available."
The open nature of the Android platform means that for skilled users, the removal of the apps from the Google Play Store is more a nuisance than an actual deterrent. For example, AdAway, one of the popular applications, can still be obtained by following the instructions on the developer's page and switching to F-Droid, an open alternative to the Google Play store.