Maybe its a regional thing and I rarely travel in the North America. I wasn't asked by Air Canada departing London for Montreal or US Airways departing London for Philadelphia. Otherwise I haven't had exit seats flying to/from North America.

I've been asked by European airlines in Europe. With one exception, I've never been asked in Asia or Taiwan's EVA air departing London. I suppose in the case of EVA it could be that I'm gold and they assume I'm familiar with things...