[brownleej]

There's one aspect of the iOS situation that doesn't apply on the Mac: Apple can't get away with it on the Mac, and they know it. It's much easier to open platforms that are closed than to close platforms that are open. If they locked down the Mac as much as iOS, you wouldn't even be able to install another operating system, which I think is fairly common among Mac users. Even if it's not common, they've used the ability to do it as a big part of their push for people switching.

Even if there are a lot of users that wouldn't object to the Mac being a closed platform, developers would. Developers want root access to their development machine. Apple doesn't want to lose developer support, because they know that it is the lifeblood of the platform.

I'd make the exact opposite prediction. I think it's more likely that iOS will allow sideloading than that Mac OS will forbid installation of software other than through the App Store. On the other hand, I can see both platforms moving toward a system where it is locked down by default, but it is trivial, and officially supported, for the user to allow installing software through unapproved sources.