Why are Clay and Boone Counties WV part of the Charleston WV MSA?

[cinyc]

Jimrtex knows more about this than I do, but which counties end up in which MSAs depends on commuting patterns. If there's, say, a Walmart near the county line, and a lot of the people in the county commute to work there, the county will get lumped into the MSA despite commuters not travelling to the central city much.

Or, at least how I understand it.