I think there is a lot of misunderstanding about what P&P means.
These days, it means the total cost of processing an order. Post and Processing, if you like. Or Post, Packaging and PayPal. There is the cost of the goods themselves, and there is the cost of transferring the goods from seller to buyer. So Ebay take their cut, Paypal take their cut, the PO take their cut, the cardboard box suppliers take their cut and the bubble wrap man takes his cut. What's left belongs to the vendor.
I don't often sell on eBay, but I do use Paypal as my main payment gateway, and everything goes by Royal Mail. Postage, especially International Postage, is my biggest direct cost. When I factor in PayPal as well, I subsidise almost every sale. I get people complaining at European, US or Australian delivery charges of £9.99. They usually shut up when I explain that it has cost me financial outlay of £17 to process the order, not including the salary of the bloke who does the processing (me).
Many people see only the stamp and are blind to the other, very real, costs.
S