I think it's something some people are naturally skilled at and/or enjoy, but i also think it's possible to "act" dominant in order to please your partner... or satisfy your customer.
That said (that's my latest segue), i don't think there would be any use for dominant partners or Masters/Mistresses, etc. if there wasn't such a demand by submissive types. Perhaps i'm mistaken, but i do not believe being submissive is something you can fake and still enjoy in order to please your partner, due to the "optional" nature of that power-imbalance. Besides, i thought i read that subs outnumber doms by... I don't remember exactly, but it was at least by an order of magnitude or two.