That's marketing for you.
Its not very often you hear of these things, unless by chance you find these things out one way or another.
I suppose its a bit like insurances of various kinds. Do an internet search, or suggest that you are leaving, and in most cases, like a miracle, the price drops.
Bremner - Will this still remain a 'rolling contract' or will BT start a new 'fixed' contract from the date of upgrade?.