Two characters or three?

Been wondering this for a while... most Chinese names have 3 characters, e.g. Chan Kong Sang, Wang Lung Wei, Fung Ging Man), but quite a lot of actors are known by two character names... e.g. Sing Lung, Ti Lung, Ku Feng, Wai Wang, Chan Shen. In all the cases I just listed it's a stage name, and their real name had 3 characters. Is this *always* the case? Or are some people given a 2 character name at birth? Is there any particular significance to having 2 or 3 characters in a name?
It's something I mainly started wondering when I started adding IDs to images, 'cause 2 character names are much less likely to return a unique hit in the DB than 3, so they annoy me :p
It's something I mainly started wondering when I started adding IDs to images, 'cause 2 character names are much less likely to return a unique hit in the DB than 3, so they annoy me :p