Well, again, the discussion isn't about an iPhone being a general purpose computer or not. It's about what happens if two sides want to engage in an otherwise completely legal business transaction(company A making apps for iOS and wanting to sell them to person B), and Apple saying "no, actually, we need to give you permission before you can do business together, and actually we'll have 30% cut from that thanks". That's where the issue is. Apple can safeguard their devices to the maximum possible extent - that is, to the point where they do not stand in the way of legitimate business transactions happening.

I've used this comparison elsewhere - it's as if a company X was making car mats that fit Mercedes models - and Mercedes wanted not only to have a say into whether company X should be allowed to do this, but also wanted a 30% cut from every transactions. Literally decades ago we made laws to prohibit manufacturers from doing exactly this. The question being asked now is - why not software platforms? What makes them so special? And yes, as a software programmer, I understand the technical issues behind this. And those issues can be presented to the courts - but as a society we need to decide if this is something we want to allow or not, this is what's happening now.

If you want to go the bad car analogy route: it's as if a company was making Mercedes car mats using the Mercedes logo and being surprised they have to pay a fee to sell them via the Mercedes dealer network.