Doctor Who has no Gene Roddenberry-like figure.

TV Allyn Gibson explains the differences between Doctor Who and Star Trek fans:

"Doctor Who has no Gene Roddenberry-like figure. Yes, Who fans can talk about different producers and different script editors, but Star Trek is, somewhat inaccurately, seen as Roddenberry’s baby, and fandom has long assigned him credit for things he had little, if any, involvement in."

In some respects Trek is like Who in that various producers have had their own ideas as to the kinds of stories which should be told. But the field is far narrower -- Michael Piller's Next Generation, Ron Moore's DS9 and Jeri Taylor's Voyager aren't that different. Not as different as Williams's Who or Cartmel's Who.

I wonder if someone could define the differences between the fans of Girls Aloud and Sugababes.

Maybe not.