Why is Scientology considered a religion?

No offense to Scientologists by any means, my question is only one of semantics, not validity. I just thought it was a little odd that Scientology is referred to as a religion (not here in the UK, of course) when it doesn't worship a deity. It was my understanding, that a religion worships a deity, else religion would not be the correct word. Surely Scientology is a philosophy, like Taoism or Buddism?