I... not necessarily disbelieve, but I am skeptical about those who say they've played for over a thousand hours. I mean do you actually have a good idea of how many hours a day you play it and how many days you've played it? Because I'd imagine after 1-2 hundred hours, it would be hard to keep track of how long you've played it.
I first played Oblivion in 2008 (beginning of) when I first got my PS3.
Its quite possible
I hardly played Oblivion at all compared to MW but had over 300 hours each with several characters
First played MW in 2005 after it was recommended to me by a friend as much better than NWN