I think they were paying a flat amount for an up to X million subscribers, not a per subscriber fee. Then they got close to the cap and needed to remove the people from the cap that weren't really using it, but the contract counted everyone that had access. It's pretty much the same thing though.
"However, the contract Starz has with Sony has a subscriber cap with regard to Netflix. The home entertainment company now has more than 23.5 million subscribers, which exceeds the cap. Starz pulled the movies from Netflix so it wasn't in jeopardy of violating its deal with Sony."