ok read up a little on the paypal site and apparently, there's something called 'chargeback' which protects the interest of the buyer. Even though the $$ has been moved to the seller's account, the buyer can claim a 'chargeback' if his goods don't arrive or the goods that arrive are significantly different from what he ordered.
I'm guessing the guy who got his credit card stolen asked his bank to claim back the funds and the seller had to return the $$. (although I still don't see why the seller has to, because he has fulfilled his end of the bargain)
It's great for buyers, but sucks big time for sellers. The seller has also done his part by shipping the products out, I don't see why in the end he has to suffer from this.
The CC should absorb this loss and launch an investigation together with the police to trace the thief. (for example thru the location where the item was shipped). Unfortunately, it's hard to do this 'internationally', even though a lot of police depts in the world are supposed to be working together and the banks themselves have branches in so many countries.
I think it's just not worth their time to recover a couple of hundred or thousand bucks.
P/S Apparently even for non CC-paypal accounts, a 'claim' can still be filed against the seller.