Whilst I agree that PB and eBay have brokered a deal to have the GSP represented on eBay, I doubt the financial interest go any further.
BTW, you are on the Ausralian boards here and we don't have the GSP on eBay Australia.
We do however frequently discuss it as many buyers come here asking about the service n costs when buying from USA or UK.
I personally stay away from listings with the GSP shown.
Too expensive and too slow. Apparently it's very good for larger items being shipped.