The main reason for KNC not including a PSU was that shipping PSUs across borders can cause unforeseen delays due to regulatory security requirements regarding power supplies.
As a customer you are paying for the PSU either way. Even if it's included in the price it's still the customer's money.

Edit: I'm not saying that HashFast is doing something wrong by including the PSU, just saying that I don't see much of a point in this statement.