Many people are reluctant to accept a faster form of payment like PayPal, credit cards, etc. because the transactions are reversible and you can't get the BTC back.
What would you think of an exchange that sold a digital object of value such as an ebook or music, then included a free amount of BTC? Since BTC are essentially "play money" and of no legal value, their inclusion would not be part of the transaction, just a freebie from the seller of the digital product.
This would mean people who paid with PayPal, etc. couldn't reverse the charge once they'd received the digital product.
Any legal issues?
Bitcoin is not play money. It is, at minimum, valuable virtual currency. Moreover, the law, as to financial transactions, follows function, not form. Financial transactions, by their nature, can be structured in creative, complex ways to avoid the letter of the law. Courts have always looked to the function of those transactions, not the structure, to determine how they ought to be regulated. Thus, an exchange that sought to circumvent money transmitter regulations in that way would probably just be treated as if they hadn't.
tl;dr: Obvious evasion is obvious.