The policy is based on the fact that many states prohibit sellers from imposing an extra charge for use of credit cards and many buyers using PayPal are paying by credit card. Its a cost of doing business and not one that can be directly passed on to the consumer (it is, of course, passed on indirectly.) Ebay will also take action if sellers indicate in the auction ad that there is a payment surcharge for the very same reason.
GatorJ 1996 300ZX NA 1970 Fairlady Z 2002 Ford Escape XLT