Comparing the 'openness' of the web app angle for the
iPad/iPhoneOS is a bit disingenuous, because you need
to have hosting ('in the cloud' or not) to deliver
such an app.
I'd argue that the very "closeness" of App Store is the reason there are about ~150 000 apps available. We see many crying how closed Apple is, but how many of those whiners would actually go through the process of getting the infrastructure in place? App store takes away the boring part and lets you concentrate on your app. And let's not forget all
the free apps hosted there. How much would it cost to self-host a popular free app?
Less than $99 a year? Including your time spent managing the infrastructure?
"closed Apple" is just another rubberstamp along "overpriced Macs" which means very little. It's just a different model and it does not make it worse, even some don't like it. There are other platforms to choose, go ahead and tinker. But whining is easier, I suppose.
Contrast with Android, which has a market with the same advantages you list (infrastructure, payment processing, search for apps, etc.), but also allows users to install apps from other sources if they so choose, at their own risk.
Note that I'm comparing the two models, not the execution - I think Apple still has superior execution, even if I don't like the model they chose.
They don't. Unless you buy an Apple phone. So if that's a problem for you, don't buy an Apple phone.