By default the .Dot is always present in every website whether we add it explicitly or not. Even if we do not add .dot at the end of bitcointalk.org or any website, the browser automatically does that for us.
On the highest hierarchical level you’ll find the root label, also called the null label, or the “root” of the DNS system. It consists of a blank area, and so is only expressed by a period, or dot. In browsers today, it’s not necessary to enter this dot anymore, since the browser will add it itself.