Today the Federal Trade Commission decided not to oppose Google’s proposed purchase of leading mobile ad firm AdMob, clearing the way for the $750 million deal to be closed. Given recent hints that the FTC’s staff might recommend the commission block the deal, the decision was something of a surprise. But as the FTC itself explained, “although the combination of the two leading mobile advertising networks raised serious antitrust issues,” there is in fact ample competition in what is after all still a nascent market.

The investigation raised several questions about not only the mobile ad market but the FTC’s stance on such deals in the Obama era. Here are some of those questions, and the apparent answers:

* Would the deal allow Google to dominate the mobile ad market?

Not at this time, the FTC said, but noted that that was a danger:

Google’s proposed $750 million acquisition of AdMob necessitated close scrutiny because the transaction appeared likely to lead to a substantial lessening of competition in violation of Section 7 of the Clayton Act. Those companies generate the most revenue among mobile advertising networks, and both companies are particularly strong in one segment of the market, namely performance ad networks. The Commission’s six-month investigation yielded evidence that each of the merging parties viewed the other as its primary competitor, and that each firm made business decisions in direct response to this perceived competitive threat.

* Are mobile ads a separate market from other online ads?

I’m not sure why mobile ads, which after all are simply ads that happen to appear on mobile device screens, are really a market separate from other online ads. Marketers, after all, usually view them as potential additions or substitutes to display ads or even search ads, and they can in fact be either of those. And if they view them as separate markets now, it’s likely they won’t stay that way as ad technology firms increasingly offer them as a package to marketers. But it’s clear from the FTC press release that FTC considers the mobile ad market distinct–and furthermore that it doesn’t matter how new it is:

The Commission stressed that mergers in fast-growing new markets like mobile advertising should get the same level of antitrust scrutiny as those in other markets. The statement goes on to note that, “Though we have determined not to take action today, the Commission will continue to monitor the mobile marketplace to ensure a competitive environment and to protect the interests of consumers.”

Mobile ad networks, such as those provided by Google and AdMob, sell advertising space for mobile publishers, who create applications and content for websites configured for mobile devices, primarily Apple’s iPhone and devices that run Google’s Android operating system. By “monetizing” mobile publishers’ content through the sale of advertising space, mobile ad networks play a vital role in fueling the rapid expansion of mobile applications and Internet content.

* Did Apple help Google clear the deal?

Um, clearly. According to the commission’s statement:

The agency’s concerns [about the Google-AdMob deal] ultimately were overshadowed by recent developments in the market, most notably a move by Apple Computer Inc. – the maker of the iPhone – to launch its own, competing mobile ad network. … 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.

* Should Apple be afraid of the FTC?

Very afraid. Or at least it should expect intense scrutiny, if the rather detailed description of Apple’s role in this market is any indication:

These concerns, however, were outweighed by recent evidence that Apple is poised to become a strong competitor in the mobile advertising market, the FTC’s statement says. Apple recently acquired Quattro Wireless and used it to launch its own iAd service. In addition, Apple can leverage its close relationships with application developers and users, its access to a large amount of proprietary user data, and its ownership of iPhone software development tools and control over the iPhone developers’ license agreement.

* Is Google off the regulatory hook now?

Not by a long shot. As the commission said:

Though we have determined not to take action today, the Commission will continue to monitor the mobile marketplace to ensure a competitive environment and to protect the interests of consumers.

Indeed, few experts believe that this decision will have much if any impact on other regulatory concerns about Google’s strength in search ads, its moves into other areas such as display ads, or the privacy implications of its vast data collection.