I find this to be the case with the "utility" type providers. Right now I'm a customer of both Time Warner Cable and AT&T Worldwide. I get cable TV and high speed internet from TWC. And I use AT&T for local phone, long distance and wireless. However, since I'm an existing customer, I don't get any of the super deep discounts that new customers get. Even though I've used both providers for years.
Both companies complain how difficult it is for them, in the super competitive realm they operate. Maybe, if they treated their existing customers as well as new customers, (or, novel idea, better), they might find people aren't as willing to jump to the competition every time the wind changes. I don't know, just a thought.