The question is, who wanted to get rid of him?
It´s like WWE or pro Wrestling in general. They all do it, and if it´s time for some reason to pull someone out, they pull him out.
If a Serebryakov takes EPO and makes a dosage mistake, and has a test at the wrong time, he gets his punishment. With big stars like Di Luca, it´s different. There, a positive sample which becomes public always has strategical reasons: federations or sponsors/private people want to get rid of him for some time, or maybe, like in his case now, forever.
That´s why Sinkewitz will think twice before returining to a 2nd cat team. He´s on the black list forever, and I think UCi doesn´t want to see him in a team higher than CT any more.