By fan base I'm guessing you mean the fan boys/girls that think beth games are the best thing since sliced bread and there's nothing wrong with the games? They are the diludeded people with more money then sense. Granted beth games are very good when working how they should but as for switching systems... If you have the luxury of owning both consoles or/and a good pc then fair enough but to go out your way and buy an xbox just because of beths lazyness is just crazyness. But I suppose this is microsofts plan and they are doing well by the looks of it.
Oblivion came out on the Xbox 360 long before there was even a PS3 for sale, let alone a PS3 version of Oblivion, so those who liked the Elder Scroll games and wanted to play Oblivion on a next gen console, brought the Xbox 360 version. Those willing to wait hoping there might be a PS3 version, waited for the PS3 to be released and the main game and
some of the DLC to be ported. Now if you have both consoles, the PS3 version of Oblivion is better, but as a fan why would you wait for a version being made for a console that does not even exist? I was surprised they even bothered getting the game ported for the PS3. I have all three version of Oblivion, I currently have the PC and Xbox 360 version of Skyrim, I will eventually get the GotY version for the PS3. But there is no way I would have brought Skyrim for the PS3 first if I could have had the Xbox 360 version. If I only had a PS3 I would have no choice. Bethesda seems to work with the Xbox 360 best, I saw no reason to change my preferred console. Especially as like with Oblivion's DLC, I was expecting Microsoft to try and out do Sony in some way.
So yes if I was a rabid fan of the Elder Scrolls games, I would have brought an Xbox 360, since that was the only next gen console on sale when Oblivion was released. As it was I brought an Xbox 360 to play the next gen version of another franchise back in 2006, saw Oblivion and fall in love with it. I would not wait 12 months extra just to play a game on the PS3, waiting extra time for DLC is not so bad. But I usually prefer to go for the console version I think is going to give me the best deal. I am a fangirl of no console, I am a fan of the games, tempt me and I show no loyalty to a specific console. Sony bothered to offer us something extra for the next game, I would as quickly buy the PS3 version first, Bethesda should have worked out how to do a decent PS3 port by then. Despite all the complaining, they did not seem to do that bad a job for Skyrim, it seemed no buggier than the Xbox 360 version.