I middle click (scroll-wheel) - I'm not sure how you're missing that point. It's literally as easy as left clicking. As for what the rest of your point is: you need to do a better job at describing what the actual intent is. Every thread in here is a hyperlink, as are all the links to forums. I didn't understand until this very post that you were talking about hyperlinks to outside sources as opposed to every link you can find in this forum (the latter would be a ridiculous request, and I'm glad it turns out that's not what you were saying).
Not knowing exactly how much it takes to edit that in these specific forums, I'd still say the effort to make that specific change would far outweigh the effort it would take every poster to use one of the other extremely easy methods of opening in a new tab.