In episode two (caretaker is one episode) the Doctor "fought" for the right to be turned off, but In Basics we find out that he can turn himself back on if he's not interested in being turned off by someone curt. In Season 3s The Swarm, they grafted the Doctors existing program onto the repair technician program (rather than resetting him, like you thought that happened, which didn't.), like a vampire, which is something that the Doctor has to do every 2 years now: Eat a hologram of comparable sophistication to live... But they NEVER talk about. A couple episodes later in Future's End, the Doctor talks about how his program recently crashed and he is still putting back together his database. The Doctor's program is self contained, and (relatively) small. If more information is added without care, or extracted without care... Have you ever played Jenga?