I've never been to Vietnam, but I'm a big fan of banh mi. However, my understanding (which might be wrong - hence this question) is that the roll is supposed to be a rice-flour baguette, or at least a regular baguette with a CRISPY outside and a LIGHT, SOFT inside. That's what I think of as a traditional baguette, and the few I've had with this kind of roll have been some of my favorites.
However, it seems like most of the "higher end" places that do banh mi (i.e. not a hole-in-the-wall Vietnamese place run by people who moved here from Vietnam) use a soft, bready roll, more like you'd find on a cheesesteak. To me, these don't work with the sandwich and turn it into something just like a Vietnamese-flavored cheesesteak (without the cheese). But the chefs at these restaurants are often renowned and have presumably done their research, and made the decision to use the softer roll.
Am I wrong, and the soft roll is in fact traditional? Is there much variation in Vietnam, so that it's just a matter of preference (like Connecticut lobster rolls versus Maine lobster rolls)? Or are these US chefs just screwing up what should be a simple, perfect sandwich with a crisp-crusted roll?