Yesterday, Steve Jobs announced that in a few months, Apple will open an App Store for Mac OS X, following much the same model as the previous – and hugely successful – App Store for iOS.

Two things are immediately obvious: first, the Mac OS X App Store won’t be the only way for users to purchase, download and install applications on their Macs; the previous, time-tested ways will continue to be allowed. Second, the App Store (as the name states), is for applications only – and only for applications of a certain kind.

The long list of prohibitions and cautions exclude, often by definition, system preference panels (like my own Quay), kernel extensions or apps that use them, complex application suites that install background processes, and in fact, anything but a plain old-fashioned self-contained application would be hard-pressed to observe all the guidelines. In fact, as others have observed, most of Apple’s own applications are non-compliant.

The huge difference from the iOS App Store is that developers are perfectly free to write software outside the guidelines, and users are perfectly free to install them. What the new App Store is promising to be is, in effect, a fenced-in garden where a certain type of user can download and install a certain kind of application while getting the warm fuzzy feeling they know from the iOS app store.

In fact, my hunch is that Mac OS 10.7 (Lion) will have an interesting change to the “Accounts” panel in System Preferences. Today, you have four types of user accounts: Administrator, Standard, Managed with Parental Controls, and Sharing Only (aka Guest). I think that all but “Administrator” accounts will allow the user to install applications only via the App Store, and that the Managed and Guest accounts will have an option restricting that user to only run applications from the App Store.

Which may not be such a bad idea after all.

For the developer, it seems that it won’t be allowed to have the same application sold over the App Store and outside it; perhaps not even different versions of the same app. That also makes sense to me. In other respects, the same old arguments apply to both the old and new App Stores: price erosion must be avoided, marketing your app in the long term can’t be left in Apple’s hands, and so forth.

As for myself, I still haven’t had an idea for an iOS app compelling enough that hasn’t been done already, and so far that same argument applies to Mac OS X apps that would fit into the guidelines; my interests lie, still, in doing utilities that enhance the system – not allowed on iOS, still very interesting on Mac OS X.