If you choose the Desktop theme on the blog, it should remember your choice, assuming you're letting the browser save the cookie. There's no direct link to the forums in the iPad theme because that theme is loaded in a 'browser window' within the app, and people were using that link to load the forums instead of the Forum button in the navigational bar at the bottom of the app (and subsequently wondering what the purpose of the app was).
If you don't use the app and disable the iPad theme, though, you should always be presented with the 'normal' version of the site, which of course contains the link to the forums that you're looking for.