Thoughts
Head on over to the Mantis forum, on this site, and you will see the same crap, people putting down each others instructors. Not restricted to wing chun, believe me!
Ive been thinking about this recently, and I believe that it has several reasons, one is to do with the lack of a strong governing body. If you look at something like the TaeKwonDo guys, they have strong international and national federations affiliated with each other. I get the impression that if I train at a TKD school in one area, I will get pretty much the same instruction in another.
Wing Chun has never had this, Im afraid the VTAA by no means represents all wing chun styles. The fact that anyone can call himself a Master brings the system into disrepute. I have seen a right load of old crap being taught, by people who should know better. In the old days, a simple challenge match would sort out the men from the boys, but this is frowned upon in western society, where much of WC is taught. So we end up with a lot of verbal mudslinging, because it is “Disrespectful” to actually question a “masters” skills.
The rise of the internet has helped fracture the wing chun world even more. Any idiot can claim that Pikachu Sifu actually is the best fighter, and learnt the secret snake dummy form from Yip Man etc. In the past, this rumour would have never got beyond a small circle of people, but now it has a literally world wide audience, and a whole world of practioners ready to challenge their words.
The final reason, I believe, is due to the nature of teaching. Most of us (but not all!) practice under the Yip Man lineage. Here is an extract from an article by Dave Peterson and Enzo Verratti called “Ving Tsun by Definitionâ€.
“It has been often suggested that Yip Man taught in a fairly unsystematic way, tending to pass on skills according to the student’s size and reach. It is also said that he didn’t have much time for his slower, less intelligent or less diligent students and actually taught few people the entire system in person. This in turn led to many people learning by observing others training, rather than first-hand, and that quite a few actually learn “second-hand†or even “third-hand†version of Ving Tsun filling the gaps in their knowledge with guesswork based on what they could recall seeing others do, or even worse, making it up out of their own imagination! This, of course gave rise to the variation in technique (and the interpretation of these techniques) extant today among instructors of the same generation, not to mention those of their younger Ving Tsun brothers and sisters."
At the end of the day, differences breed competition. You go with what you are taught, when faced with anything else which looks or sounds “funny”, it is human nature to feel it is bound to be worse. 
Its a tribal thing
Us and them!
Thats my take on it, any how.