You can't always type 1000 word posts. Even you're 'good.' Even on the advanced RP sites. Do you honestly think someone can think of tons of paragraphs every single post when it only calls for answering the above person? Just as you shouldn't have two-word posts or one-liners. You shouldn't bloat the posts either. You don't see full blown 'back to the past,' scenes and off topic thinking in every book if the characters are just talking.
Sometimes, it calls for short. Casual, advanced, whatever the level, it's still better for short at times.
Not really. Chances are, if you can't think of more than a simple thousand words to express what you need to say, the topic's done with. I thought like you did once, but once you RP on a site like that you start to see the point in it all. The fact is, SP is really, really casual about stuff. That takes away from a lot of its realism and art.
In any case, what Iaz said.
Also, this is kinda an IC contest sort thing to promote active roleplaying formality. It's not a fanfiction kinda thing or an exert so much as RPing on the board and somewhere in an RP here with someone else, you write 1,000 words in one of your posts.