My take on 'commercial grade'.

The biggest difference, with regard to polish, is that commercial apps are made by a purposefully assembled team. You have designers, UI experience folks, coders, QA, etc. With Open Source, the skills of people in a project is (nearly) random and that's why it's such a gamble how it turns out. It is also the reason why bigger projects often look better - they simply have a bigger skill base to draw on, with better chances of someone filling a gap. After a point, this turns into a loopback - good software draws more people, which again means more potential contributors/skills. Also, a super-important point is that you people remember SUCCESSFUL companies/apps, not the (lot larger number of) those that went under or never produced a decent piece of software. We had plenty of commercial applications on Maemo that were utter cr@p. Maybe just 0.1% of applications on the iPhone falls under what you call 'quality apps', but these are those you remember and equate with the iPhone 'experience', forgetting the remaining 99.9% that is useless.

PS. And sure, you might say trinket class software and simple games are often one man shows, but that does not influence skills. If one guy can do all the aspects of software publishing (which is pretty rare), he'll be just as good in whatever approach he takes - commercial or open source.