We do have the subsections you're talking about. They're created by Tags.
If you want to access a certain Tag, you can do it pretty easily by using the URL. For example:
... will take you to all posts tagged with pre-1500.
If there's not a tag for what you want, you can create it on the fly when you create a post.
Also, if you want to keep track of the tags that interest you most, click the big + sign in the corner of the post list for the Tag, and it will add that list to your Favorites. You can do this with individual posts, too.
To find your list of Favorites, scroll to the bottom of any G2G page, and you'll see the My Favorites tab.
Of course, you can always add your Tag to your profile page, too, and then you'll get a list of other genealogists who are also following that Tag along with some other useful information, AND updates will be emailed to you as well.
So, it's actually pretty cool forum software once you discover all the features. ;-)