Yes, if a bitcoin exchange accepted credit cards, they'd be on the hook for any chargebacks. Hence why most of the existing exchanges want a bank transfer instead.

In theory, a bitcoin exchange should have a near-perfect defense against chargebacks for faulty or missing products or similar, by showing via the public block chain that they delivered the purchased product as requested. However, there's no defense against chargebacks claiming that the cardholder didn't make the purchase (stolen card number, etc).