reading the article, seems that the old e-gold would also qualify as hard digital currency (by the criterion of an irreversible transactions)
e-gold is a "fairly hard" currency, but it's still centrally controlled so in principle transactions could be reversed. It's only due to a policy decision that they aren't. This is in contrast to an anonymous cash transaction which cannot be reversed (without initiating violence).
Bitcoin is somewhere in-between those two. A transaction can only be reversed by action taken by >50% of the computational power of the network.