ShipScript has been an eBay Community volunteer since 2003, specializing in HTML, CSS, Scripts, Photos, Active Content, Technical Solutions, and online Seller Tools.
We are asking eBay staff the same question. As one would expect, only actual buyers can leave feedback, so "verified purchase" is a bit redundant. One staff suggestion is that it instills buyer confidence... and that may be the actual reason, since people are influenced by phrases to which they are accustomed. There is pushback on this, so I suspect this must play out further.
eBay has provided an official answer to this question:
"We understand that experienced buyers and sellers on eBay may view the additional text as unnecessary. However, before implementing this change, surveys with eBay users showed that half of them didn’t know that feedback can only be left by those involved in a purchase. This text removes any doubt."
