Thanks for bringing this subject up, VI Edit. I too get into argument with people about it. In my view, Midwesterners have an accent too. I agree completely with Mwilding and Jellomencer.
"Technically, the Midwestern 'accent' is standard American English (as distinct from British English). So to be technical about it, Midwesterners do not have an accent. (Note that I am not including the Upper Peninsula of MI or areas of northern Wisconsin in my definition of 'Midwest' as the U.P. and northern Wisconsin both have accents that are uniquely northern.)
On the other hand, if you want to play fast and loose with the definition of 'accent', and claim that an accent is any manner of speaking that is different than the manner of speaking the same language and the same dialect, then yes, the Midwest has an accent."
Speaking of technicality, one should start with definition first. The technical definition of accent is (from the Oxford English Dicitionary): a particular mode of pronunciation, esp. one associated with a particular region or group; style of pronunciation of region or social group.
Everyone technically has an accent. If we followed your definition, then if an individual of a different ethnic group grows around, say, the English people and adapts to the English accent, then he has not accent because it wasn't of his origin. But this isn't so. Midwesterners do have an accent as do everyone else. You can argue that they can't be identified, therefore they have no accent. But if this were so, then you have a paradoxical situation. If one can identify one by their accent, then how could you tell that they were Midwesterners? If it weren't the case, then why would there be dictionaries with phonetics or why would the speech experts be able to train one to speak a certain way with pronunciations? There would be no such thing as phonetics for the Midwesterner and no such thing as training one to "lose an accent" without adjusting to another accent in the process.
The only logical way to make an argument that Midwesterners have no accent would be if one sets that as the frame of reference by which everyone else is judged. But if we do that, then what stops us from using the British accent as the frame of reference for the English language?
And I should add that it isn't true that Midwesterners are any easier to understand. They're like any other group of people. If you bring someone of a different accent from a different region who speaks English perfectly well but had never met a Midwesterner, never heard Midwestern music, never watched a movie with Midwestern characters, for instance, that person would have as much problem understanding the Midwesterner during his (or her) first encounter.