You see this in every game in some way or another. If a GM wants to run a Super Hero game there is someone who wants to be a villain or resistant to being a hero. If you want to run a Rebellion game they want to be working for the Empire. If you want to run l5R or Fantasy Samurai, they want to be the gaijin.
You can see this already starting up on the Fantasy Flight Game boards where people are sad/disappointed that it seems like the Age of Rebellion game isn't going to have rules for playing Imperial Characters.
The thing is, I'm not necessarily sure what the thought process is behind this desire. Now, I don't think it is wrong. In fact, considering one of the key pieces of advice for players is to stand out in some way than claiming something unique (i.e. a gaijin in samurai land) is a good way to do it. Beyond that though, I'm not sure I understand the thought process.
When a game is made to do something, and the GM is putting a game together to do that thing, what is the draw to doing the opposite? Is it just standing out and feeling special? Or is there something more to it? I'd love to hear your reasons why.