I think it comes down to whether the term "Wagyu" is legally recognised and protected in local law. Unless it is, anyone can call any random piece of beef "Wagyu". Which isn't to say that some farmers, like the ones you linked to, aren't doing it properly, more that you can't trust that every instance of Wagyu is from a genuine Japanese breed. For example, this article (http://www.theage.com.au/victoria/wagyu-farmers-beef-with-fakes-20120922-26dvq.html) suggests that Australia has rules, but with no enforcement a lot of people are flouting them.

I mean, Asda Wagyu? Do they think that's Japanese for horse? ;)