You are quite wrong. Most companies are not about openness and community. They're about profit. Apple retains the right to not allow your app on a phone, or to retroactively pull your app if they change their mind on it. They also have failed to approve apps that have had great user demand (like tethering and book apps). That's not open, and it's certainly not community driven. Just making an SDK available doesn't make you open. Things like the kernel speed patches, JoikuSpot and Mapper are freely available on the N900 because it's open source. Such things will never show up in the iApp store, despite them having almost identical hardware.

No.. openness means you're free to do what you want with your device. You're not leasing it, or renting the software, or granted a temporary license so use it until the company that made it changes it's mind. You own it, it's yours, you can re-sell it, destroy it, or change it in any way you like, just like a book. In the case of the N900 you're also free to pick it apart, since they hand out huge chunks of the code that runs the core of the device. Try making a kernel patch for Windows some time and you'll see how different open vs closed can be.

The disclaimer for 3rd party apps is there to make sure you're aware that what you're doing is something not specifically approved or coming from the manufacturer. It's a courtesy warning, distinguishing what's 100% approved by the company vs what's community. Think of it like a "Windows approved" sticker found on some hardware boxes. It shows that the people who made that app/device went through the extra steps to meet special requirements set by the manufacturer, nothing more.

Having come from other phone that were not open, or that missed the mark on how much should be done by the company vs community driven (Google: Neo Freerunner), I can tell you that Nokia has done a really good job. It did what it said it would do out of the box. The browser is great, the media player works for almost everything I've thrown at it, and it works like a phone too! Anything beyond that is icing on the cake. At this point, there's almost more icing than cake.