The maps are of ash that is actually deposited in geological formations, so the talk of wind direction is somewhat immaterial - if you notice, the ash spreads in a fan from the source, with some going out at right angles to either side of Yellowstone, an event that huge could make its own course in the form of pyroclastic flows.
No, talk about wind direction is not immaterial when dealing with ash fall out....
I live in So. Cal I've seen it rain ash in a big way...For days at a time....And where it rains ash my friend, it's directly dependent upon wind direction.