That seems weird.
In the US, I've seen hydraulic brakes on F-800's with 30K GVW. In fact, one of my buddies who's an excavator owns an F-800 30K with Hydraulic disc brakes.
Also, trailers can be quite large and have electric brakes. I've seen 3 axle trailers, even 9 tonners with electric brakes and they work OK, just not as good as air. I'm thinking about buying an electric brake 9 ton trailer.
Check again, Dave. The road rules are very confusing. Even most government highway workers & cops don't know the rules correctly.