I really don't think it's that simple. Things I believe but can't prove:

* Open Source Usability, just like OS security, engineering, marketing, QA, translation, installation, update schedule, funding model etc. etc. will be different from the closed source analog. Doesn't make either "better" a priori, but does mean you can't transplant one to the other wholesale and have it work the same, nor can you easily compare one against the benchmark of the other.

* That Open Source Usability will in fact follow your two steps with a crucial difference. It will still involve super awesome frameworks that do everything but will be followed by figuring out how to expose different subsets of those features in multiple UIs. Potential case study the UI horror that is Evolution (because it tried to copy proprietary Outlook) spawning multiple new frontends like the pimlico suite that expose just contacts or calendar and the new Anjal mail client:

http://blogs.gnome.org/sragavan/2009/03/18/announcing-anjal-...

* Corollary of the above: if you're copying a proprietary UI wholesale then you're probably doing it wrong. Steal the ideas yes but re-interpret them in a way that makes sense for open source platforms.

* iTunes is a usability disaster since commercial and proprietary pressures have forced a CD player, CD ripper, music library, internet radio, online music store, party music player, network jukebox, video player, iPod manager and god knows what else into a single app. This is actually the anithesis of Apple design principles but is forced on them by the need to push their stuff onto Windows. If you're working on a music player for the Linux desktop, for the love of god, stop copying iTunes.

* Safari/Webkit is what it is because it a) started with code from KHTML and Mozilla, b) continues to be an open source project that is used as a component in multiple applications, including two completey different browser UIs from Apple alone (Safari and Mobile Safari, the latter being a far more impressive UI. Safari itself is mostly just minimalist, and that's why I use it, with a few odd gee-whizz features thrown in.).

* There's plenty of good software on Mac OS X that adds well thought out Cocoa UI onto a bunch of existing open source frameworks and libraries. Writing stuff from scratch is stupid when the libraries are there for the taking.

* OSS and Usability focus are not in conflict. When Panic were so anal about their UI for Mac OS X app Coda that they decided to include a programming font they based it on an open source one. This is not a zero-sum game. Mac OS X is shot through with open source from top to bottom, 1st to 3rd party.

* proprietary pressures can corrupt user interfaces. (See iTunes example above) Why doesn't Internet Explorer have spell-checking? Because it threatens Word. Why doesn't Microsoft Office warn you that it's going to remove all the formulas from your ODF spreadsheet? Because it threatens their standards hegemony. Some proprietary software constantly gets in your way because it is trying to impose its will on you. User hostile software is not known for good UI.

* Usability without function is worse than function without usability. Recent example: Ego iPhone app breaking because of a Google API change
http://log.maniacalrage.net/post/98510137/a-little-over-a-we...