You sure are. You just linked to an image showing that Memory Stick Pro was a joint effort between two companies...that's already counter to the definition of the term as it relates to technology. That Sony was the only major adopter doesn't matter.
No, it isn't. Just because it was developed by two companies doesn't prevent it from being proprietary in the technical definition. And again, colloquially, the word "proprietary" has come to mean something different, and you'd be remiss to ignore it completely.
Beta and MiniDisc are proprietary technologies because they were developed and controlled by a single company...despite other manufacturers producing their own Beta and/or MD units. Memory Stick started out proprietary (as I mentioned earlier) but hasn't been for years.
Again, it's not about a single company, it's about the copyright holder issuing licenses to other manufacturers. Are you actually going to argue that the technology behind the Memory Stick has been made public domain by Sony and SanDisk?
There seems to be a problem on this board with regards to reading comprehension and logical thought progression.