Yes, I am aware of that. That's the Census Bureau's opinion. This is about what Atlas thinks. There's a Texas thread on the off-topic board. The Census places Texas in the South, but many say Texas is not completely Southern. It's not as if once you cross the border from Texas into New Mexico that the regional landscape or culture instantly changes (though I suppose it's possible sometimes).
I don't completely agree with the Census. I disagree with classifying Maryland & Delaware, but not Missouri, as Southern.
Anyway, I agree that the 4 states in the poll are mostly Midwestern overall. However, there is obvious Western influence. Where I live, both sides of the SD/MN border appear the same, but the western part of my state is more Wyomingish.
I agree that MD, DE, and MO don't really belong where they are anymore- but they did when the Census first came up with this grouping, and you kind of have to keep it from census to census for statistical continuity. But, yes, Maryland and Delaware have been getting steadily more Northeastern, and Missouri more Southern.
All the other states are clearly in the right region. Yes, along the Great Plains you have a nice long edge case where the western bits are more Western and the Eastern bits more Midwest/Southern... but seeing as the eastern bits are more populous, if those states can only go in one basket the Census has put them in the right one.