Well. There are subs and there are submissive people. They are not always one and the same. I, for instance, am very much a sub, but I am not a submissive person. I am opinionated, mouthy, uppity, obstinate, and generally difficult. It takes a very good dom to keep a handle on me for long, and hold my interest. (I can say this with confidence and not hubris after years of experimentation.)
That said, I don't play subs. I play people. If they tend to be more submissive, so be it. I play Cinderella in a thread, and she's a bit of a dreamer, a little shy and slightly timid, put into a situation where she feels out of her element and thrown off-balance. Submissive? Maybe... but difficult to picture someone who wouldn't come off as submissive in that situation.
In another thread, I play a woman up for becoming a SEAL, who's just basically trying to get what she's earned. She's been in some submissive situations... but she is not a sub. She's also a person, with her own likes and dislikes.
*grins* It's all about what you enjoy, after all.