I understand your position and don't see open source as a the solution of everything. Please notice that my opinions are from the point of view of the platform (WebOS) and not from the phone or hardware.
But WebOS (an operating system) is under a situation where the main developer (HP) has discontinue it. This is a risk that we have in the software industry. I had seen a lot of software turn into abandomware, into a legal void that nobody can know even if they are using it legally or not. Just try to remember IBM OS/2.
The hard question for the WebOS community is "What choice do we have right now if we want a future for the WebOS platform?"
Open source software reduce the risk of the vendor dependance. If WebOS would be complete open source today, now we will be seeing companies, possible big, possible small, saying.. don't worry about HP, we will grab the source and legally continue to produce new version of WebOS (..under another name). But that is not the current reality.
Just see what will happen with the Linux community if RedHat or Novell when out of business? It is legally and possible that other company will grab RedHat and Novells Linux source code and support the customer that were left behind. This does not happen with close source/propietary software.
I know that possible many people like WebOS because they saw HP strong arm behind this, and possible will be people quitting WebOS, just because HP is no longer maintain it. HP was one of the few companies that can get inside the iPhone/Android/WinPhone market and compete...but the situation is different right now.
The only way that I know (as today) to reduce the risk that this uncertainty is producing to the WebOS platform is open sourcing the OS. (under an OSI approved license)