Take Usenet for example, it got overrun by spammers and trolls because there was no real way to block them and the few moderated groups basically meant a few people were in control of the discussion. Instead we moved to forums, where you could use CAPTCHAs and various other tricks to block mass sign-ups, moderation, flagging of abusive users and so on. They're not perfect, but they work okay.
Why do so many people use Facebook instead of email? Same thing, much less SPAM. For the longest time, Linux users hailed the repository model over the Windows "download random exe from the Internet" model. Then Apple took it to the extreme with the "one store to rule them all" and suddenly it was a problem. Even on Android you have to pass by huge warning lights to enable third party repositories and Windows Phone has as far as I know joined Apple in the "one store" model.
My guess is that they'll push it to the cloud so all the application code runs on a server and they just need to lock down the browser, more per user&app sandboxes, more difficult time running unsigned software and more users with computers that need Apple's, Microsoft's or Google's sign-off to run an application. The average user simply doesn't understand the micromanagement involved, same way users won't use NoScript when browsing the web. They'll "outsource" it.