Most states requires a Foreign Corporation registration, or something to that effect. So, if you incorporate in Delaware, but live and perform services for that corporation in say Tennessee, the corporation would need to be registered in Tennessee as a foreign corporation (i.e. one not originally incorporated there) and pay a small registration fee.

Not a lawyer, but I think that's it, outside of paying the appropriate employment taxes and fees to the employee's state of residence/operation.

I'm guessing this is what the article's author is referring to, but the way he explains it sounds like someone advised him to incorporate wholly owned subsidies in the states where he had employees, which would be both unnecessary and more expensive.

You would have to file for "operating authority" for an out-of-state corporation, which typically involves similar fees and paperwork to incorporating in-state. I think that's what the article is referring to.