Would it not be in Vodafone's best interests to offer the Sure Signal to people on alternative ADSL providers, and charge a premium? Surely there's a market of people who want one, but are more than happy with their current provider.
I can see the business case for enforcing Vodafone broadband (I have a Sure Signal with Vodafone NDSL) but wouldn't the market for them be much greater if they could be used with anyone?