Or it was a number they picked at random.

Or it could be a reference to Pearl Harbor (there's also the homage to "day which will live in infamy" on the page).

Rofl you noob If Cataclysm comes out in November that would be too late! Blizzard said it would be in a PRE-cataclysm patch! Can't Wait looks fantastic!

Funny! :D
So was not picked random. Hello... out of all the numbers in the world they pick 12.7%.
Come on now?

Random is random. It's possible, yes, but personally, i'd presume "imminent" would mean sooner than that. I'd expect it to be out by mid-may if it was "imminent".

Even more telling...

December 7 is a Tuesday!

if it was any other number they picked then you would wonder why they picked it

"The chance of any CATACLYSMIC EVENT"
If 12.7% is a date that Blizzard are hinting at (I don't believe it is, as Blizzard is an American company, meaning that would imply 7th of the 12th, which is way too late in the year, considering they're giving out beta keys to the press) they would be hinting at a date they're releasing Cataclysm, as Deathwing bursting into Azeroth and completely ravaging it is "any cataclysmic event", not the retaking of Gnomeregan ;) (jokes aside ofc :P)
Either that or it'd be a date they're releasing the patch (like 3.0.1 came out before WotLK) which is when Deathwing would actually cause the cataclysm, rather than the expansion itself.

Then again, 12.7% is a random number, I wouldn't go all speculation on it :P (to respond to coolbam13, it has as much chance as 12.8% and 12.9% and 12.6% and 12.5% and 12.4% etc. Unless you're saying there's something special about that number? O.o)