There are a number fo very important points here:
What is Wing Chun??
1# to some it is simply a collection of techniques and principals.
2# to others it is a group of forms and nothing more
3# To others its is a principal in itself, a way of thinking that expresses itself in a fighting situation (I belong to this thrid group)
What is Ground Fighting??
To me ground fighting is a range that is available to every art, be it okinowan, be it kempo, be it Tai Chi, now although there are some arts that deal almost exclusivly with ground fighting, ground fighting is not exclusive to those arts.
The goal of a Martial Artist is to transcend the limitations of his own art, to lay hold on its fundamental expression, and learn how to adapt that into a fighting situation. If you look at your art purely in this manner you will loose long term, but if you learn how to lay hold of the essence of the art, and run with it, you will find that whether or not it is kicking, striking, Trapping, grappling, or ground range, you are able to take the tools and principals that you have extracted from your art and utilise them in this situation. Sure it may not be as effective as BJJ in that range, but that does not discount its effect.
Arguments such as WC is ineffective in Ground fightning (and even if this thread did not start in that vein it will get there) are moot, of course its effective, the question is not whether its effective, the question is its degree of effectiveness, when compared with specialist arts such as BJJ. But that is only one aspect, there is another.
In terms of the ground, each art has different goals and strategies wheree the ground is concerned, and it is in light of those goals that the art trains. For example in Wing Chun the goal is to control the fight so that you do not end up on the ground. Why? Because to truely be in control you must stay on your feet (unless you have the luxury of fighting one person only [a rarity in todays world] but if you end up on the ground there are a number of factors that you should take into consideration; Terrain (I dont like rolling around on broken glass); Possibility of multiple opponants
When you go to ground there are a number of unkowns, that you need to be on guard against, thats why the goal in Wing Chun is stay of the ground, this is why the stance is meant to be developed properly, and the sui lum tao is so vitally important, many people underestimate the true nature of the SLT, but maybe that is a good thing. However if, if, you do end up on the ground then you must be prepared to do what you must
to get back on your feet not stay on the ground. Now BJJ may have a different goal, but that is BJJ, not Wing Chun.