one thing that is often overlooked in the comparision between something like boxing, and wing chun, is that (more often than not) boxing is something that you may do for a relatively short period of time, whereas wing chun is something that people (least I plan to) be doing their entire lives.
That way it actually makes more sense in terms of Boxing being the way it is - it teaches you to fight, with contact, because that's what you are learning it for, and that's what you will do with it (i.e. - get in a ring, and actually box.) If you are boxing, your chances of getting hit full contact are alot higher, as you are going in there with the intent of that.
With wing chun, alot of people do it for a lot of reasons - from health, to coordination, to self defense etc etc etc. As an instructor, you have to be able to cater towards all these types of people. Particularly when looking at some of the internal aspects of wing chun - these just take TIME.
If you want to take wing chun to a place where there is alot of sparring and alot of contact (and I'm not saying that is a bad thing) the onus is on you to find training partners to go and do that - the onus is not on the instructor or the style.
Anyhow - just my thoughts.
'If someone wants to fight you, run a mile. If they are still behind you after that, run another mile. If they still want to fight, and it is really worth it, turn around and beat the living !*$!% out of them, 'cause they will be really tired.'