tardtasticx: yeh if you read it, it says "no extra to pay, nothing to sign", so they are legally obliged to go with this.
It actually says "There's nothing extra to pay, nothing to sign and no obligation to keep it after this time.", i.e. after the 12 months. Is there an obligation to keep it before the 12 months expires? I'd have to read the offer T&Cs to know, but I wouldn't be surprised. I guess they would expect you wouldn't want to leave since the deal is so good.
With regards to the asking nicely idea, they can't make you stay with them so all they can do is ask you to. That's not to say that if you don't, there won't be some penalty. You'll certainly lose your treat, maybe that's all, maybe not.