I disagree with you completely. The more proficient your team is on a specific operating system, the more expensive it's going to be to move to a new one. My focus is on RedHat based distros, since that's what's used in the business world. If you asked me to admin a Debian site, or a Freebsd site, or a Solaris site, I'd be absolutely able to pull it off, but my productivity would suffer for a while.
For example, right now I could build a Cobbler host and Kickstart a hundred machines inside of a day or two. If you asked me to do the same with Jumpstart or FAI, the same simple task would probably take me a week. I could absolutely do it, but as a consultant the real cost to my company for moving from Centos to Debian based on that project alone, would be thousands of dollars.
I did switch from Fedora to Ubuntu on my desktop machines. There was definitely a learning curve, and I'm a little slower with system management tasks. It was justified, since Fedora was fairly broken on the equipment I was using. I'm happy I made the switch.
On the other hand, if I was fairly Junior, the cost of switching OS would be lower. Since I'd have a learning curve ahead of me either way, it wouldn't really matter which way we went.
None of this is a complaint about Debian, or Solaris, or BSD. They are all competent and powerful operating systems. It's just an illustration of the potential issues.
I'm very very surprised by the strong reaction I received to my original post.