I will cry the day that a closed ecosystem device becomes peoples' primary computing device.
However, I wouldn't be too surprised to see a completely closed Mac/PC ecosystem in the future. Not now, but in the the next 5-10 years. As things move more and more "to the cloud" and the desktop becomes a dumb terminal, the easier it is for Apple to just tell everyone that they must go through the App Store.
They did introduce that dialog which warns you when software is not signed, but of course MS didn't take this to the degree that Apple has. While it's a great way to take care of malware, I really don't think Apple's vision of the future is one I want to compute in.
You can set Windows to only allow signed applications to run, too: http://technet.microsoft.com/en-us/library/dd723683(WS.10).a...
That 90% of the population you're talking about really is using "personal computers". The iPad is just a "rented" piece of hardware, which you can use only in ways that pass Apple's approval. That's pretty far from "personal" to me.