Cablevision Systems Corp. Chief Executive James Dolan said the number of customers paying for the traditional big bundle of TV channels is going to shrink by about 20% to 25% over the next five years, as consumers opt instead for smaller packages of channels or online video options. Mr. Dolan warned an investor conference Tuesday that the reduction in subscribers is "going to have an impact on the programmers" -- the big media companies that collect fees for each customer who receives their TV networks.