Also, remember that piece you linked to is dated from 29th August 2010. Over six months ago and things change, maybe that's how Moffat originally envisaged it, but since then, both himself and the Beeb have said it's just one season split into two.
That's the point. He changed his mind half-a-dozen times about whether last year was Series 5 or Series 1, so who knows when he'll change it agian!