For some reason, reading the post doesn't mark it as read and you have to comment. That just... doesn't make sense.

It does mark it as read. Unread threads including threads you've been to which now have new posts on it will have an icon that looks like overlapping speech bubbles. Once you view a thread and all new posts at that time, the icon disappears. The check mark is for when you've commented on a thread.

In addition to what said, you can also mark a post as read without actually reading it. There is a button at the top of every subforum that says "Mark All As Read". When you click on it, it will turn green, say "All Marked" and bounce a little. Then when you refresh, you will see all the little thought bubbles have disappeared, showing the posts as read.

Most of the forums I look at are in advertising, so the new comments aren't usually relevant. I'm looking to mark the post itself as read, not the comments.