iAd is an obvious-feeling exception to this, of course. That said, iAd has clearly never been a focus, it's always felt like an "I guess we should," and maybe a poster child for WebKit in the commercial/ad space, but not as a significant means to an end for the company. How often is iAd discussed by Apple or anyone else, especially compared to everything else they do.
They also sell content in their online stores, but that is also a false lead, because it differs from Google and social network styles of digital monetization. They're still selling CONTENT to CONSUMERS there, and they're only doing it because they want Apple hardware to be the thing people buy to consume their media.
When selling iCloud, they have repeatedly pointed out that its an advertising free service. "Who wants ads in their email?" was the sentiment expressed at its announcement.
Apple suddenly shifting gears, turning their precisely built, paid for and profitable consumer goods into trojan horses for bundled adware seems nearly entirely unlikely.
Letting users INSTALL that sort of thing wouldn't be a surprise -- "Siri, play 'Super Troopers' on Netflix" -- but that's, again, the user using a paid for service or product on the device, not the user being sold to an advertiser.