What..... I'm from the Midwest and it's not any different than anywhere else in the US for me.I find this more myth than fact. In my Midwest city portions are rather small. Perhaps it's different in the south or in NYC.
Also, I agree that it could be a chain thing, but I've often found non-chain restaraunts overdoing portions.
I used to go to a small Italian cafe every weekend for breakfast and the portions we're usually on the spot.