Unless it is a whiteboard which runs Perl, it isn't really an environment :) Personally, I haven't been asked to do any code in an interview (I make sure I send examples and a link to CPAN before going in), but have been asked to do pseudo-code and flow charts.

I think if I were asked to write actual code on a whiteboard that were more than any simple one-liners or few-liners, I would say something like "When I code I am generally on a computer. Writing code an a whiteboard is like taking a bath in the kitchen sink.. not the proper place to get it done correctly."

I must say, I found the whole thing disconcerting, and I'm not sure what it says about my grasp of what I know.

You know what you know! Interviews can be stressful as it is without pop-questions which you need to answer on a white-board in front of people which you do not know. But, being able to write code in an editor other than vi would be useful, in case it isn't available to you at some time.

Cheers,
KM