Also, 2012 Q1 posted a 494,000 net subscriber increase before the 348,000 loss in Q2 -- so it's still net positive on the year.
Source: »paidcontent.org/2012/05/11/pay-t ··· d-in-q1/
It's only been relatively flat the last couple years, and that's largely a reflection of the economy.
Still, when you have 100 million subscribers in the US paying for TV, it's pretty easy to see why you'd want to make a device that would appeal to some of them.
Note that the major area of growth is TelcoTV, and Verizon is still using QAM delivery for TV, hence a "cable box" would be usable for them as well.