Quote Originally Posted by dps View Post
I've always been somewhat skeptical about there being a requirement to use the Daleks every series/season, but people are constantly telling me that there is. As far as what the show-runner has to say about it goes, well, Moffat lies. A lot. I don't trust anything he says anymore.
The way I was told is that there's a bit of copyright weirdness with the Daleks where they don't technically belong to the Doctor Who franchise, but instead belong to the guy that created them. The original contract stated that Doctor Who had the right to use them as long as they appeared in at least one episode per season, and if they don't appear the contract lapses and the full rights return to the owner, who could then charge them an arm and a leg for any future appearances.

How true this is I have no idea, but it's plausible enough.