As opposed to the five star trek series we actually got that were full of people, none of whom (bar the odd non-regular character) were from our time? I'm guessing you don't watch any of the Star Wars films, or Battelstar Galactica or any number of sci-fi shows that featured entires casts not of our time.
And of course any historical film or tv is also out because you can't relate to the characters in them?
No, I don't think you understand where I'm coming from. As far as I'm concerned, the Doctor is the alien element in the equation, and the Companion's role is to anchor the show in a recognizable reality and perspective, and to serve as the de facto point of view character. When the Companion is a caveman, a robot or a talking penguin, you lose part of what makes the Doctor Who formula successful.