That's a really great summary. It's an interesting alternative way for companies to produce a fair amount of open source contributions and still make money. I can definitely see this with other companies including ones that specialize in continuous integration and other services that developers are interested in.
Companies like CoreOS, Mesosphere, all fall under this umbrella, where you could technically glue all their open source components together to form their main product, but it would take you quite a bit of time to support.
Github is sort of like this. They contribute a ton to open source, and are built mostly out of open source components (that ARE open source). But their website is really just a glue to all their infrastructure, and that's closed source.