They act to refresh the forum page. One says "Forums". Another says "DawgTalk". The third option is "Dawgtalkers.net".
They each take you to different levels of the site. It has nothing to do with revenue or anything else; it's just breadcrumbs for site navigation.
"DawgTalkers.net" is the top-most level. It goes to the site root.
"Forums" takes you to the top-level of the forums. Since we don't have a portal or other sort of main page that the forums would fall under, this is functionally the same as "DawgTalkers.net", but if we had a portal or main page, then they would be different.
"DawgTalk" is the DawgTalk category. You'll notice that when you click it, the Archives category is no longer visible. That is because it exists at the same level as DawgTalk. The inverse happens if you go to view Archives; DawgTalk won't be visible. Click on "Forums" and you'll see both DawgTalk and Archives.