Yes you called the question stupid, and no you did not understand it. If "you pay USD go USD to BTC to buy", as the poster suggested, how do you send USD to Coinbase/exchange/Bitpay/whatever?
How about this:
I send the USD to the exchange in any way it's available to me, preferably with the cheapest one.
It could one of these:
ACH for Coinbase
Plain wire transfer (most of the exchanges)
Or even these:
Astropay (Bitstamp).
SEPA (Bitstamp, Kraken, and so on)
...
The point is, even if there are middle-man fees with all these methods, you will end up with BTC, which in turn gives you more purchasing power (due to discount, offers, etc) than you would have if you used USD directly.