It's been like that for a looong long time, ntl have always been concerned about reducing churn, but it does actually make sense. It can cost more to get a new customer, than keep an existing one. Just think of the installation costs to ntl alone.
The only real issue is how many people phone with no intention of moving. They are playing with fire because if ntl were to call their bluff
Would be nice to see some genuine offers for long term customers though, without having to resort to underhand methods to save some pennies.