As I see it, the Intel switch was mostly important to get Macs being used (and thus recommended) by geeks for the same reasons it's been popular among non-geeks: the ability to run Windows (and, of course, to a lesser extent, other Intel operating systems).
This, along with the increasing importance of the web (and thus lessened importance of the specific OS platform), the spread of Apple retail stores, and the iPod/iPhone halo effect I think are the main reasons Mac sales have done so well.
Because of that mix, it's hard to tell how much the platform's openness has been important to it. It certainly hasn't hurt any, though, and it's a very likable trait in a "desktop" OS!
Mobile apps tend to be "bite size" (approachable), centrally discoverable through the App Store, very low cost, be built around rich media, and the user feels a control over their management that makes the experience more like the "lightness" of visiting a web page than the "heaviness" of traditional desktop app management which is marred by unpredictability, multistep install processes, reboots, conflicts, and a general feeling of lack of control. I think users really like software... they just hate all the bullshit overhead that has usually gone with it.
Apple owes a lot to standardization and opening up. It's not all App Store lockdown. The question is, is this App Store crap a general trend? Are they going to bring that to the desktop?