> You would be surprised how many third party companies support closed source software product of another company. This is very common in enterprise world. It is also a common way for a vendor to get their foot into an enterprise entrenched with a competitor's product.

I'm aware of that, and have even worked with such companies. However, IMHO it's way harder (and less effective) than supporting an open source product. For instance, it's way harder for a 2nd or 3rd party to diagnose and patch a bug if they don't have the source.