They're highly conservative, in practice, and often work to supress newer or better ways of doing things. Heck, for decades you couldn't get a bagel almost anywhere in the US except New York because the only people who knew how to make bagels were members of a union, which kept the recipe a secret. But those bagels are really not anywhere near as good as the real thing from New York, even today. While not a guild in the traditional sense, or in the sense the article uses the term, it serves as a reminder that my business is largely an oral culture. Sure, there are books, but they don't have everything you need to know, and you learn primarily by apprenticing in deed if not in name.
Few things are harder to put up with than the annoyance of a good example.