Yes, but what I think is going on is some cross referencing between the actual size of the movie project and the export. The FCE/P editor in me thinks this will have to do with pixel aspect ratios. But eh well.

Edit: I want to append that iMovie has some pretty concrete options for project size. It's 16:9, 4:3, or 2:3. That's all, folks. So if you have 2:1-type widescreen, iMovie won't play nice at all. You may have to look elsewhere. Even FCE would be rather set in it's ways, but there are more there....