Open Source – “Because we can fix it if it breaks”

My current project at the time involved building a Single Sign-On architecture. A key requirement for the project was it had to provide capabilities for sending and receiving SSO requests to and from their partners.
We, (my team at Cogent Company) had it all mapped out using Windows Server along with Active Directory Federation Services (ADFS). We even found a great partner that could handle the integration of Windows with other platforms (i.e. IBM, SUN, Linux/Unix, etc.).
Our best laid plans were soon changed when we started working with my client’s partners. They decided against implementing our architecture (which would require minimal changes to their code base) in favor of open-source technologies. One partner’s justification for their decision was, "because if it breaks, we can fix it".
Nice. If only their boss could have this rationale. What manager or executive wouldn’t want their people fixing open-source software?  I wonder how this situation would play itself out in actuality? In their status report would they cite as their reason for not completing their work as, "unavoidable delays caused by the need to correct open source the open-source application we chose that doesn’t work?"
I realize this attitude is not shared by everyone who prefer to use open-source technologies. But in my experience I have run into enough to decide this attitude is just plain stupid.
Why not just implement something that works once deployed and is backed by a real company…not a bunch of techno-wizards that like to experiment with their  code?