EvgeniRocks, I don't think you are ridiculous, and if you see Plushenko as a two-time champion, good for you. However, moviechick is correct that in the sense of common use of the English language, an Olympic champion or title holder is the winner of the event. This is why Plushenko's Olympic profile, which I linked to before, does not list him as a two-time champion, but as having won one title. I would posit that the IOC is the authority on this matter, not the Union Internationale de Pentathlon Moderne.
Also, when in doubt, check the dictionary - in this case, the Oxford English dictionary:
champion: • noun 1.
a person who has won a sporting contest or other competition. 2. a defender of a cause or person. (Emphasis mine).
http://www.askoxford.com/concise_oed/champion?view=uk
Evgeni Plushenko is a great and accomplished skater, but a two-time Olympic champion he is not - as of 2008, as you noted. Personally, I hope he doesn't become a two-time champion, and if I had to pick who will win in 2010, I'd say that barring injuries and/or a meltdown, it should be either Takahashi or Joubert.