Brian
I suspect that most people would look at a system for example, that has chi gung, joint locking, ground fighting, sweeping/throwing, more weapons, etc to be "complete" or at least "more complete" than styles that lack one or more of these things. It can be argued, as I know it will, by many wing chun practioners, that wing chun has all these things so I will provide the reply "has these things in a way that is more developed"
to those who would say but it only "seems" that way, well, then I have no reply other than I disagree haha
maybe alot are. Maybe there are those who stay with wing chun because they don't care for those extra components ie joint locking, ground fighting, etc
maybe that's why people cross-train. sytems that cover vast ground and many areas may be suffering from the "many swords but none very sharp" syndrome. perhaps it's better to learn less "complete" but more specialized systems since they perfect one area, and look elsewhere for systems that specialize in other things, perfect other areas.
and of course, maybe some don't see wing chun as incomplete. whether they are mistaken or not is a different story...