[ubernostrum]

Open implies working with products from more than one vendor.

But "open source" does not imply that -- it implies that you will have access to the source code, and the rights to redistribute and to make/distribute derivative works.

Or, to maybe drive the point home in a different way: if, say, a game is released under an OSI-approved license, but for sake of speed contains some inline assembly, would you then claim it's not really "open" since it only runs on a single CPU architecture?