David Sparks discusses anti-Mac prejudices he has experienced when presenting at various functions.
Many (but hardly all) of the IT professionals serving these industries have been far too busy earning Microsoft certifications to pay any attention to Apple and they are not only unhelpful, they can actively lob hand grenades at your attempts to get any work done with your Mac.
I have a number of friends and colleagues who work as IT professionals who, seemingly, have similar anti-Mac biases.
Macsparky is on the money with the idea that Microsoft Certifications, at least in part, at the core of the problem. Microsoft has done a good job convincing employers that they should hire people with these skills, and thus lots of IT specialists chase those certifications.
In my own pre-Mac days I undoubtedly had similar biases. But it is certainly my own experience in the past six years of Mac usage that plug and play functionality is stronger in Macs than in Windows machines.
I personally try not to present if I am forced to use a Windows machine.