But HTML5 is an increasingly interesting prospect for developers, Systrom and Hamoui said.

FORBES: Why Start-ups Are Building Mobile Apps First

Omar Hamoui, who founded Admob, which was acquired by Google, recently founded Churn Labs, to specifically incubate mobile app companies.

FORBES: Why Start-ups Are Building Mobile Apps First

" As for what Google and AdMob are going to do about it, Hamoui would only say that they're going to be "speaking to Apple to express our concerns about the impact of these terms.

ENGADGET: AdMob CEO responds to Apple's new advertising rules: 'not in the best interests of users or developers' (update: Greystripe responds)