Thanks for the clarification.
I wasn't sure what would be the case here (I agree with you it being a "service" in a generous sense of the term!), but can see the logic being applied here.
It'd be nice if the wording was clarified on their side. After some digging around, wording is inconsistent - I've seen mention to change fees of $100 plus taxes, and then no mention at all of amounts not taxes charged on cancellations... but I suspect that's more poor copy-editing than anything else. Mildly annoying, but hardly surprising.