Apple, thwarted in its ambition to buy AdMob when Google swooped in at the last minute, subsequently bought another mobile ad company, Quattro Wireless, in January.
In a statement about its decision to conclude its inquiry into Google's proposed acquisition of AdMob, the Federal Trade Commission cited Apple's entry into the market as part of its rationale.
"As a result of Apple's entry (into the market), AdMob's success to date on the iPhone platform is unlikely to be an accurate predictor of AdMob's competitive significance going forward, whether AdMob is owned by Google or not," the FTC said.
The FTC's decision was driven not only by Apple's plan to launch its own mobile ad service, iAd, but by Apple's access to proprietary user data and by "its ownership of iPhone software development tools and control over the iPhone developers' license agreement."
Apple CEO Steve Jobs has defended the decision by claiming that dependency on third-party tools hinders developers' ability to deploy Apple technical innovations.
The FTC said it would continue to monitor the mobile advertising market for possible antitrust issues.
Google said it was pleased with the decision. "As mobile phone usage increases, growth in mobile advertising is only going to accelerate," said Google VP of product management Susan Wojcicki in a blog post. "This benefits mobile developers and publishers who will get better advertising solutions, marketers who will find new ways to reach consumers, and users who will get better ads and more free content."
At the Google IO developer conference on Thursday, Google VP of engineering Vic Gundotra previewed several forthcoming mobile ad formats, including click-to-call ads for mobile content and ads that expand to fill mobile device screens.