"GM fiat" is a bullshit term. (No blame! It just is.) Descriptive improvement isn't subject to GM fiat -- that's just bullshit.
Descriptive improvement is the GM's call, legit and aboveboard, subject to the GM's agenda and principles.
And my only principle is "Michael never gets what he wants". So cool.... :)
But yeah, I hate it, too. That's why I'm not comfortable with it. I hate it being on me as far as people's "improvements". I mean, we're all "roleplayers", right? We'd never ignore the story and just push for improvement, right?
So when someone wants something, it's not my job to make sure he doesn't get it. But it's also not my job to give out shit like Christmas candy, either. The players know that, so they've ALWAYS got a legitimate reason for wanting it. And I hate telling them yes or no.
I'm a robot automaton, Vincent. I NEED clear instructions, preferably in punchcard format. :)