Why is that a problem? You don't have to use all of a programming language for it to be useful. UML is just trying to "unify" a bunch of useful diagramming under a common umbrella.

I agree with you and Fowler, sketches are probably a better use. When UML came about I think designs were largely developed before hand by architects/analysts and astronauts and given to developers to implement as is, but now they are better used to aid in documentation or spec out specific interactions/concepts that belong to a larger system.