said by MrMoody :

Yes. And why are they losing subscribers? Competition from FiOS and UVerse? Puhleeze, they're still a drop in the bucket and DirecTV/Dish have been around as video competitors for ages.

I think there are three primary reasons:

1. Semiannual increases far exceeding inflation cause people to get fed up and unplug.
2. ATSC is a such a huge improvement over analog in many places, people who try it on their new widescreen TV wonder if they really need a $60 escalating cable bill for an inferior picture. So unless they need HBO or ESPN, they unplug too.
3. Comcast's legendary poor customer service drives customers away as well.

said by TKJunkMail :

Comcast keeps losing basic video subscribers.
...
But the continual loss of basic video subscribers is a trend that will eventually cost them down the road as they have fewer and fewer cable connected customers.