I don't think tying claims need to prove an actual monopoly, just the somewhat lower standard that the seller has sufficient market power in the tying product's market for the tying arrangement to restrain trade in the tied product's market. It's been applied in the past to car manufacturers who tried to corner their own cars' replacement-parts market, even though the manufacturers didn't actually have a monopoly in the car market.

It's hard to prove, though, because it tends to require showing that the company did the tying solely or mainly for the purpose of restraining trade, as opposed to for some legitimate purpose. The car manufacturers lost because the courts didn't buy their argument that their attempts to limit the replacement-parts market were for quality-assurance reasons. Apple would have to argue that section 3.3.1 isn't intended mainly or solely to stop cross-platform compatibility, but has some legitimate, non-trade-restraining purpose, like improving the reliability or quality of iPhone apps. Probably even just "it makes it easier for us to review apps if they're all in the same languages" would be a good enough explanation. A bad result would be a leaked smoking-gun email saying "hey we should institute this policy to stop people from porting our apps to Android".

Monopoly leveraging is a separate (but related) concept, as far as I understand it, and a bit easier to prove, because there's a much stronger presumption that if it's happening, it's bad, regardless of the reasons.

(Edit: edited/expanded a bit for clarity)