It's your fault, sad to say. In order to become a vampire in Oblivion you had to get hit by vampires while fighting them. What's more, you either didn't see or just ignored the part where it tells you you got the disease. Then you played for 3 days without noticing the effect, and then you slept. It isn't the game's fault. Also, did you just use a Cure Disease spell or potion after you slept? After the 72 hours that doesn't work, but if you did the quest, it is still your fault.
I think they are in, in fact I would bet all my internets that it is true. It is a staple of TES, I just hope they combine the elements of Morrowind and Oblivion (Passing for human in Oblivion, an actual culture and society in Morrowind).
So I don't become a vampire randomly while sleeping?, gotta admit I didn't know that XD.
Being a vampire wasn't all bad, I just thought I was being very unlucky while sleeping (Nice bit of info that a vampire had to touch me while I was awake), the vampire sight really came in handy in some quests (Pitch black dark prison where I had to avoid guards, hard as hell without night vision).
I hope both of them are in XD.