If I had to wager a guess, it's that NCSoft didn't want to cannibalise Blade & Soul with two MMOs having overlapping themes.
That, or it's to reduce interference during the Chinese launch.
it's probably a little of both, but definitely this.
Tapping Asia comes with 1000 shards of glass that NCsoft will make Anet walk over making sure everything is ... 'Kosher'.
I'm positive we'll see Cantha, but it won't be till GW2 is being played in the Orient.