>Users of English who can only understand a narrow range of accents (Americans, I'm looking at you!)

Is this based on your anecdotal observations, or is this opinion based on something concrete? Because as an American who knows many other Americans, my anecdotal experience is that we can understand English accents from people all over the world.

This of course varies from person to person, but software engineers I've worked with are accustomed to speaking with people with accents.