That's a pretty poor justification. If Google were serious about protecting users from this loophole thy wouldn't exploit it.

Whether the bug is fixed by the Chromium team or not, Google should not have been exploiting it to track users.

"This tracking, discovered by Stanford researcher Jonathan Mayer, was a technical side-effect — probably an unintended side-effect — of a system that Google built to pass social personalization information (like, “your friend Suzy +1'ed this ad about candy”) from the google.com domain to the doubleclick.net domain."

edit: to be clear, whether or not is was an intended side effect, it is a side effect of a (potentially) legitimate use case (setting the value of +1-ing an ad aside).