great observation!

this will be a part of our subreddit spec, but theres a subtle difference:

you might not want to post a topical microblog to a subreddit. also subreddit posts have titles, etc. you will be able to create both types of posts simply by adding a title or not. The latter is posting to a group for all to see, the former is just for your followers.

still working through the UX on this, but they are subtly different things.