My plan to combat this in any future interviews (and a couple of previous ones) is to bring my laptop with me. If there's any development questions, I'll do it on my laptop. If they become offended that I want to develop in my preferred environment, on my preferred keyboard layout (Dvorak + capslock->backspace), with my preferred editor... they have failed my interview. It ought to be a plus that I came that well prepared.

Incidentally, having been on the interviewing side, I do not see this often enough. Bringing your own laptop ought to be something you always do. I can provide "a" coding environment but it won't be "yours". Unless you always develop in a completely uncustomized standard Visual Studio environment, maybe (in which case frankly I'm still wondering a bit...).