Ebay states specifically that the seller cannot charge the buyer PayPal fees (specifically. You can, of course, bury them in your item price or shipping fee).
Ebay existed for a long time on money orders alone, and later on both money orders and PayPal. It's only recently that they have become PayPal only (though you can, as a buyer, request to send a money order and the seller can agree. The seller, however, cannot OFFER to accept paper payments. eBay really has their hand up our behinds with that one.)
I had an X.com account (later became PayPal) since 1997. I've been
through every policy change PayPal has ever instituted. They're the big dog, so they can pretty much do as they please. Especially since eBay has their sellers by the gonads. Anywhere else, though, the buyers and sellers and site owner can make their own terms for PayPal usage.