There are MANY different type of sexual sessions.
Lovemaking: Tender, intimate, "I love you and the sun revolves around you and my life would be nothing without you. I can't wait to grow old with you."
Just sex: This is, "We're both horny, we want to have sex, we're going to go have sex." This might include less romantic positions like doggy-style or trying weird kama sutra upside down stuff, usually sex toys.
Fucking: This is like the "Just Sex" one, only it's rougher. There's some dirty talking, there might be some light spanking or hair pulling. This might get a little ex
Scene play or Role Play: A lot of how this plays out is up to the submissive partner. How they like to be dominated, what's allowed to be said, what's allowed to be done, which implements they like to have used. A good or creative Dom/Domme will take the parameters that they're given and create a scene or experience for their sub.
These times are as intimate, sometimes MORE intimate than just "Love Making." The reason for that is there has to be complete trust on both the D and S's part. The sub has to trust that the Dom/Domme will not do something that is outside of what is allowed. The Dom/Domme must trust the sub to use the safe word/signal if things are not pleasurable AND must trust that the sub gave him/her all the parameters.
My husband and I feel closer to each other after a BDSM session than we do on Valentine's Day or our anniversary. There is just so much involved. It takes thought, planning, love, trust.
There is a time and place for each and every one of those sessions. If you've never engaged in a BDSM session, then perhaps you're looking at it with myopic viewpoint. Perhaps joining in our
Basics of BDSM meeting that @VieuxCarre is hosting tonight will help you to understand a little more about the lifestyle. You should also read this article that P'Gell wrote for the EdenCafe. It's very telling of the intimacy involved. I would encourage you to understand that it's not insulting if the person who is being dominated asks to be spoken to. They feel love because their Dom/Domme loves them enough to give their sub what he/she is asking for.
But a scenario as you described above of a loving scenario turning that dirty like *snaps fingers* that? That is not how it happens, it's not how the dirty talk is integrated. It's not sporadic at all. It's very carefully thought out and planned out.