I used to think this too for the cases of Virtual Goods, but Paypal surprised me. Our company suddenly started getting Paypal chargebacks resolved in our favor one day. Not all of them, but more than the zero we previously had.

We have a fairly large number of transactions per day, so I can only assume that our account got flagged somehow.

That said, Paypal only sides with us if it was a transfer of Paypal balance. If the transaction was backed by a credit card, and the credit card was charged back rather than done via a Paypal dispute, we will lose every time.