"The ui bits" is an understatement, because UI & builtin apps is actually where the meat is, and they know it. The kernel, Qt, the standard desktop stuff, etc. they are _forced_ to open, unless they want to violate the GPL. But whenever there is anything they're not forced to open, and someone else could potentially have an interest to actually see the source, then they keep it closed. It's actually less open than Android!

You can also have pure SDL apps on WINDOWS, out of all platforms, so what is the point? And sure, there is also value in that, but "privacy" value?