One payment processor, Bitpay, has said they don't sell their coins on the open market. They have private buyers for them.
Bitpay partners with Bitwage, who provides Bitcoins to anyone receiving a paycheck via direct deposit. Simply setup your direct deposit to send a percentage to Bitwage's deposit account and you receive Bitcoins to your wallet address every pay cycle. No action is required to withdraw your Bitcoins. They are sent to your actual on-chain Bitcoin address immediately. It is essentially Bitcoin direct deposit. It circumvents hostile banks that might try to keep their customers from sending funds to Bitcoin exchanges. This allows for a complete cycle wherein Bitcoins spent at merchants who do not wish to keep them are then sent to Bitwage's customers rather than being converted to fiat currency at an exchange.
I never really understood the reason for doing this. If you want to convert a certain amount of pay into BTC every month simply setting up an account with an exchange and sending the $ amount you want to buy over every month, works out to be the exact same. The only thing I can think of is the Bitwage path is automatic, but manually buying on an exchange isn't exactly hard and probably results in less fees. Both paths require you to provide your banking and personal information so there isn't an advantage for either one.