So Wizards of the Coast, not satisfied with having a really long company name, has taken to making video games with excessively long names, too. Last year, they released Magic: The Gathering: Duels of the Planeswalkers and mtg-duels-of-planeswalker was created as a way to fit most of the title into the 25-character tag limit.
Not to be outdone, they released a follow-up this year, Magic: The Gathering: Duels of the Planeswalkers 2012, a functionally different game that really does need a separate tag. Unfortunately, duels-of-planeswalker is 25 characters, so the "2012" can't be tacked on.
I asked a question about it a few days ago, and the tag mtg-dotp-2012 was created as a way to distinguish it from the earlier game, with the justification that "DotP" is sometimes used to refer to the series.
But the plot thickens: in trophy lists and in reviews, Magic 2012 is used to shorten the name of the game, and quick Google searches seem to indicate it has some good SEO (especially since Wizards of the Coast is also releasing the Magic 2012 core set for the physical card game at the same time).
P.S. There's also a case to be made that duels-2012 should be a synonym too: WotC has used that shortened form in its FAQ for the game for example. But "Duels" is such a generic name, and I doubt many people would search for the game using it.