Differnt types of roleplay (couldn't think about anything better)

[Brook V]

I've been looking into roleplay at LiverJournal but never joined anything. Then I found this place.

This is just a thought I've been having and I wonder what the rest of you think?

The RPG's I've been looking into at LJ is mostly fan-based, kinda. You take a pre-made character from a TV-show, Book, Anime/Manga etc. and play that character. I haven't seen many OC's on the games I've been following at LJ.
What'd you think of pre-made characters?

The RPG's I've been looking (at LJ) into is panfandom/multiverse types of RPG. However all of them has a closed room scenario i.e. you're taken from your home world either by unknown magic force or get to a place in your home world. In none of these cases you can get away from there. You're stuck.
Why is it like that? Why is it that you get to a place and have no way to get back?

On this site almost every RPG is with OC's.
Do you think that is better than pre-made chars? Why?
Is free-form i.e. a world where anything can happen, better than an (original) existing world, with rules and a pre-defined setting?