If there actually is a D2:ED release that uses a CD key, then they may be able to refuse honouring their money back guarantee. Depending on the details, though, that could be more support for a false advertising argument, since they did not specify what version of the game the CD key was valid for.
In any case, if they do consistently refuse a refund, Paypal/etc may be more sympathetic. If not, you can at least go through the process; maybe enough people doing so would encourage a change, or attract the attention of a business ethics or legal organization.
