I don't think this is so much a question of liability as it is one of customer perception. If 'GoDaddy Secured' sites aren't really secure and start getting hacked, then 'secured by GoDaddy' signs will mean no more than "hackable in 10 minutes or it's free". We'll see how GoDaddy squirms when that happens.
I think that beyond customer perception, there is an actual question of legal liability here. If GoDaddy is purporting to be an expert in security and selling a service, that is supposed to ensure security, then they should be found liable for some degree malpractice.
I'd love to get a real lawyer's opinion on this...
