As far as I'm aware, these all have equivalents under Mac. However, you may need to change your licenses which would be another financial argument.
What (apart, of course, from financial) are the aguments pro and con? Most students probably use little more than Office. We do teach computing in the sixth form and things like Dreamweaver, Fireworks and scripting are covered. All, are fine, of course, on Mac (aren't they?).
The SIMS client won't run on a Mac, simple as that. You'll either need to keep some PCs, dual-boot the Macs, or have something like boot camp. Alternatively I suppose you could look into SLG. I suspect the same applies to a lot of general educational software though.
We have SIMS, used by all teachers as well as most admin staff. There is the odd thing that Macs may not hack such as the software and hardware in our Multimedia suite (used by Languages). I bet there are other things I haven't thought of.