What if you want to update a value, but you want to store the number of times it was updated to be returned in the JSON (not idempotent, but not an unreasonable thing to want)? Would you still use PUT?

My point is not that the ascribed meaning of POST and PUT is bad, I think the concepts behind both these functions are great, but what if you want to make a different or more complicated function? It makes sense to me to invent your own rather than be limited to what HTTP gives you.