We get a lot of requests from project teams about how they can use Stack Exchange to support their communities, so we do end up with a lot of "official channels" pitching in to help the folks who are asking about their products on our current sites. But their role does not include any ownership or other type of control over the site. Their participation is like that of any other community member motivated to help folks with problems they've likely seen before.
We have been approached for various types of "partnerships" to create a site, but they don't usually go anywhere because we require ceding so much control back to the community. We've never been contacted by Apple, but we have become an part of the official support for Microsoft's MSDN; same for Android Development. You mentioned Ubuntu. We have a site for SharePoint, Wordpress, Drupal, Salesforce, Blender, Mathematica, Windows Phone, Arduino, and about a half-dozen content managers, but those were created by the grass-roots efforts of their community, and those sites have no official ties to the project at all.
Sites on Stack Exchange are ultimately created and built by a community. If you have a project that you would like to see supported in Stack Exchange, most project teams find it better to support the subject as a tag on one of our existing sites. But if you have a project that doesn't fit any of our current subjects, feel free to propose it. That doesn't give you any special privileges to impose specific rules or to brand it with your logo or anything like that. But if you have a large community enthusiastic enough to build and support a new site, you can start with the proposal process in Area 51.