I believe that e-bay were worried about buyers not leaving negative feedback for fear of negative feedback from the seller.
when i first started buying on e-bay, i got feedback once i paid for the item (normally immediately after the item had ended), now i get feedback from most sellers once i have left feedback.
Now i can leave negative feedback and not worry about the seller doing the same. I think the seller can still reply / post a comment on any negative feedback left by buyers.
Brendan