I also agree...
There is never any harm in trying to get a discount, however, if one is not available, you always have the option of changing supplier/cancelling and re-purchasing.
The most obvious (to me) answer for NTL is to offer the same deal, providing you take on a new 12 month contract.
The fact that they don't do this is annoying, but no different to any other business.
in summary (my opinions

) there is never any harm in trying to get a discount, and if you fail, then there is still no harm done.
If you are unhappy, change supplier (even if it is to the same supplier

)