From what I've seen, you can ride damn near anything in a brevet. I'd bet the vast majority of bikes in brevets are not rando-specific. For my money, I want a bike that's going to go straight when I'm wasted. "Turns on a dime" is not what I want when I'm seeing things and trying to remember my own name. Other people -- many other people, by the look of it -- don't care so much. C'est la vie.