I really do prefer the sound of my amp mic'd, but I never demand it, and I'm always courteous about it and inform the guy in plenty of time. Sometimes it happens, sometimes it doesn't. Unfortunate if it doesn't, because most of my sound comes from my amp (I'm sceptical of a lot of people who say 'my sound' with a straight face for 'normal' bass tones, but my bass isn't almost fully driven without an amp to do it...) and my DI on my amp doesn't work properly!
If there is a reason why you can't have everything your way though (having an engineer who is incompetent and will probably make things WORSE by doing it how you ask is included in that), then you shouldn't be a dick about it though. Just get on with it and play the gig. Live sound is never perfect.