Well, see, it's a tricky one; I'm a slave (at the moment, although have Dommed). The first thing is to define 'belittlement' which I know the OP has specified as a phrase used to exert dominance over another person. However, belittlement in itself is quite litterally something to make another person feel small, to put them down, or to humiliate them. These two can potentially be very differant things depending on the people involved. For instance, Sir has some very innocent ways of verbally exerting his control over me, none of which involve any form of belittlement in it's most litteral translation.
However, having said that, a lot of couples do enjoy humiliation play, including Sir and I to some extent. To me, begging is humiliating, but it's something we play with (mostly with orgasm control) and it's a very effective way for me to remember exactly who this body belongs to. Would that be called belittlement? Not necessarily. Humiliation play? Possibly. Verbally asserting control? Absolutely.
The other thing to consider is humiliation as a punishment. If the submissive of a couple sees humiliation this way, then belittlement could potentially be a punishment, which alters it's translation entirely. It's not just about asserting power, it's about inflicting emotional pain, which is never completely necessary. I'm a 24/7 slave and desperate to please, and I can honestly say that Sir has never needed to punish me. I couldn't cope with being belittled and put down as a form of punishment; I'd take it too much to heart.
Having said that, however, I know that not a whole many relationships conform to the same level of intensity, many people having a part-time and more casual relationship. So the question arises of how exactly does it differ?
Anyways, I suppose the short answer is that it depends on your definition and, more importantly, on the people involved.