If you have multiple ISPs selling connectivity over a carrier-neutral set of wires, they're going to be trying to poach each others' customers whenever they churn. Any business with high customer churn carries high marketing costs because the return on marketing is relatively good with 20% of the market up for grabs every year. With more players doing marketing in a zero-sum system, overall marketing spend is likely to rise, not decline.

All I'm saying is that the marketing costs wouldn't go away even if the big cable companies do: they would just be replaced by a dozen smaller companies doing the marketing, billing and connectivity. These smaller ISPs would just be taking each others' customers rather than customers jumping ship to DSL or some other last-mile tech.