Jeff Corbett posted today about your rights to something you've posted on a third party site. He disabled comments, but suggested that anyone with opinions write their own post and link back.
Active Rain is more liberal than most sites - and if they are giving us the exposure they do, why shouldn't they have some rights?
Our posts and even our comments are often picked up by google. So - regardless of our "contract" with Active Rain, by posting, we're allowing our writing to be public. Even on our own sites, we can delete content, but perhaps the deleted content was captured by another site that captures what was on our site at a given point in time.
When we change companies, the former franchise may demand that we remove all references to their company - we can't always do that - a site that connected us may no longer be "manned" or able to be contacted, but the connection is still out there.
The internet is a public domain - once we release our writings to the internet, we may no longer be in control. This is not meant to address plagiarism, merely the cataloguing of what we wrote.