I'm with Lisa. If you are an original Doctor Who fan from back in the day, then you are accustomed to the frequent actor changes. It's a bit like soap operas. I don't know what they do nowadays, but when I was an ardent fan back in the 80s actors were switched out all the time. Who can forget the deep voice intoning, "Today the role of Doctor Johnson will be played by James Jones" at the beginning of a scene that featured a replacement actor?
I am also a fan of Torchwood. Poor Tosh never catches a break, does she?