Linux is a nightmare to maintain as an IT department for end users, especially with hardware incompatibility problems and software availability. This is clearly an unsubstantiated article based in speculation.
Though I do not have significant data myself.
I did a transition for a company back around 2003. Total cost of transition was a net saving already in the first year. Including training, my work, minor new hardware, etc. A couple of their guys learned the systems maintenance enough to take over my work, so I made myself redundant. Just like it should be.