(To respond to your first comment for a second: I run open source projects that have tens of millions of users, so I know quite a bit about the feeling on the other side of that specific issue: those text messages I mentioned I get all the time are about bugs in something I distribute for free under the BSD license.)
You are now conflating "prorietary" with "charity", which is ironic at best, and seem to be disagreeing with my arhument not because you disagree with it's logic, but because you dislike some indirect ramification to a cause you believe in, which is sad. :(
Open Source is not some magic bullet that makes something fundamentally maintainable: it simply affects the cost of one option, which is accepting the lock in and operating the project yourself. 99% of the time it will be cheaper to take another alternative, like "migrate to another solution", which is certainly something you can do with a proprietary solution.
So no: I disagree with you; if you are choosing an open source project just because it is open source, you are a bad businessman. Example: if you chose mod_python for your web architecture today--a discontued (with prejudice: the sole remaining official maintainer hated it) project that I seem to be the only remaining user of and which (honestly, despite what I tell people) wasn't very good in the first place--over a proprietary alternative that actually had a working business model, like ASP.NET, solely because you could maintain the former yourself, that would /clearly/ be a very poor and highly costly decision for your company, and would easily allow a competitor to run circles around you on cost of development and maintenance. There may even be reasons why mod_python would be chosen over ASP.NET (such as a plausible, if painful, migration path to mod_wsgi combined with the now know to be incorrect preference of coding in Python ;P), but this one in specific is simply irrational.
As for Digium: an ecosystem (like Skype) is fundamentally different than a hosted API, and I'm confused as to why you feel it appropriate to compare them... I can replace Google Translate (an API I rely on and do not regret choosing), but I cannot replace Skype, even if the entire client were open source.