Makes perfect sense. Somebody will be providing an ad blocker no matter what. If it is Google then they get to control how it works, why it works and when it works.
Build whichever browser components remove barriers to entry for users (ad block, compatibility with many existing web apps, better performance/stability/ease of use, etc.) => build widespread adoption => commoditize desktop operating systems.
It's been a while since I last had cause to use the google toolbar but didn't that have a adblocker?
This news doesn't seem all that surprising.
[edit]Just realised I'm mixing pop-up blockers and adblockers. I don't think this makes the parent comment any less valid.