I am from Indianapolis and regularly have people not know anything about it so I dont find this to be an exaggeration. The anecdotes really ring true for me so sounds like you arent from the midwest.
Greetings fellow Hoosier. It has been my experience as well at west coast conferences, some people think we are all from some redneck farm in the middle of nowhere. I think the close mindedness says more about them than us.
I recently moved to Idaho, the other I state. People occasionally call it Iowa multiple times in the same conversation! Similar to that Ohio/Iowa shirt, there's also an excellent one sold at the hipster grocery stores in Boise that has the outline of Idaho with some lovely drawings of a farmer working a field of (presumably) potatoes... IOWA is printed across it in huge, bold letters. The Idaho<>Iowa confusion must extend past my circle of friends and coworkers.
That being said, I'll freely admit I don't know where Des Moines is inside Iowa's confines.