There was a Doctor Who RPG, once. It came out in a normal paperback size format, and was about as popular as a randy dog at a Miss Lovely Legs competition. I can't remember who published it but the game allowed you to play the existing doctors and their companions up to Sylvester McCoy's Doctor and Ace.
I think the problem was that it did not allow much variety for the players. The characters were set in stone and the chances of them actually dying were about zero. My group refused outright to play it and I think I gave it away in the end.
Even with the ressurection of the Dr Who TV series and its rise in popularity the problem remains as to what sort of characters you could play. Apart from the Doctor the Timelords did not go swanning around time and space at will ( apart from a couple of exceptions like Romana ). So if players can't play Timelords that relegates them to being companions, second fiddle to an NPC Doctor.
Torchwood brings more possiblities to light as they mention on that there have been other Torchwood projects than the one in Cardiff. This may not be as universally popular as Dr Who but it allows a game with all the favourite heroes and villians to put in an appearance, while allowing players some freedom in character creation. It could even be Welsh if you like.