Your points are excellent, no doubt about it.
I provided Mac support for a full service communications department for 9 years, so I'm well aware of the voodoo involved with these types of users. (This is also where I learned to hate Quark and its rotten business practices.)
The idea I continue to reject is the "all or nothing" concept. I think it's good business to set up a Mac OS X workstation or two and bring them online. See what they can do in your particular environment. Use them for your Photoshop work, to create your Flash animations, for Illustrator jobs, etc. If they're on the network and contributing, as they can in so many ways, then the switch can be an evolutionary process instead of revolutionary.
You could manage the costs of upgrading applications as your budget allowed. There are many low cost alternatives too, especially for personal use, that we are gathering up to write about. Those articles will show you that you can have tons of power for little $$$.
I'll say it again: a little ingenuity goes a long way.