Of course I know about those commands, I also realized that posting before had a link. I just wish there would be no need to use them. IOW, maybe someone would change the forum's default themes back to normal behaviour.
The forum pages aren't normal web pages because they use different code (BBCode, forum software, etc.) to standard HTML code so that people can make posts.
Because of the the tag that is usually associated with links, the <A> tag isn't present, that is what applies the default underline on links and also what allows scripts to change the effect, different colour, no underline, etc.
So without the <A> tags, the browser when it complies the code for the layout of the page it doesn't see any <A> tags so it doesn't apply the normal standard underline, or any other effect if there is a script on the page to change it.
Links in the forum pages (view page source) usually start with [ url ] (spaces to avoid code) a non-standard HTML tag. See this topic that goes into it in a little more detail
http://forum.avast.com/index.php?topic=24679.0 if you try using the using the forum underline command inside the [ url ] tag you will get some strange looking results