I think they're a mixed bag, probably depending on some customer profitability / value score. I've heard other people complain about trouble when packages were stolen, but the few times it's happened to me, I've gotten replacements overnighted without even having to talk (chat or phone) to anyone.
I've always found Amazon customer service to be amazing.
Seriously, I can't think of any other company where it's as easy to get a real person on the phone. Or a refund.