I have different expectations from my iOS device and from my Mac. My main work machine must give me the freedom to install whatever I want, since limiting this freedom would be crippling. But I don't require this of my phone, since I don't see the added benefit. This is a practical point of view, and I bet it is common among developers.

Perhaps in the future most development will take place in SSH sessions on a remote machine, and then closing down the Mac will not longer be a problem, but I don't see how that would work today.

There wasn't a wide variety and large number of native software titles written for iOS before the App Store.