If it was just a matter of him gifting software, Steam wouldn't really care. If you pay for a $5 dollar game and gift it to your buddy, Steam still got the $5. I want to say that I don't have all the facts, but the article said that the guy was Russian, and if I got the context right he was gifting to people in other countries. If this is the case there could be a value disparity due to currency conversions and if this person was actively using this disparity to make money at the expense of Steam then I would definitely see Steams justification. Normally a company would just sue the offender if they felt they had a case, but in this situation Steam had the right to axe his account, so they did.
There are two different issues here. These are ethical questions, not legal ones as we already know the legal answers. First, should Steam have the right to cut access to your legally purchased software based on suspicion alone? Second, in the event there was fraud taking place, what mechanism is in place to deal with said fraud? If he is Russian, does that mean that Steam would then have to petition his government to allow a civil case, even though he broke no Russian law?
Personally, I think Steam should just stop allowing gifting of games to people who reside in different regions.
Again, I only know what I read on it so if someone has facts that are different than the way I understand it please post them.