Thank you for the respond Egol,
Right, but original .com version is not deindexed (!?) and that is the issue at the first place. They are manufacturing links and it works for a long time now. Their .com website still ranks high.
As you have said 'Google has been killing one of those pages or the entire site for a long time' - killing ONE of those pages or sites is not sufficient enough. What about the original page/site which still ranks? Nobody cares for their duplicate websites being deindexed.
Than you have said 'In the long run you still only have one site, sometimes it will be damaged by these efforts.' - well, the one website which ranks is all they need :). If 'sometimes' will be damaged, than it still means that it is OK to manufacture links by duplicating website, and take the risk to 'maybe' become deindexed.
Theoretically every website owner can create duplicate websites and manufacture tons of back links. It makes the white hat link building pointless. If you ask me this is very much violating google's policy and they should be reported. Otherwise, why don't all of us do the same!?
It is irritating to see someone acting spammy getting better rankings...