Using the broadest definition of 'cult' you are correct, Cofty. But most people don't mean that when they use the term. When a believer uses the term 'cult' he usually means something like Vanderhoven7 listed - doctrinal and theological stuff outside of mainstream Christianity is considered a cult. When a freethinker uses the term 'cult' he usually means any group (religious or not) that uses psychological thought reform on its members (Lifton's seven principles or Hassan's BITE model or one of the other models out there). When a sociologist uses the term 'cult' he merely means an offshoot religion that most of us would call a sect.
We're all saying the same word and meaning different things.