Spitoon, I can't really reproduce the 60-page "Laws and Rules for Glider Pilots" published by the BGA. The exemptions and differences from power flying are part of the ANO and/or Rules of the Air, in various Acts and Statutory Instruments. As I am not a lawyer I don't profess any specialist knowledge, I just look things up that I have not learned by heart if I need to.
I used the term "somehow exempt" because that is how the original questioner phrased it. The ANO/RotA are where the exemptions are defined, albeit possibly in somewhat elusive terms. Unfortunately, "Laws and Rules" does not always reference the exact clause so I can't easily quote them. I think flying in cloud may be related to privileges of licence and CofA of the airframe, but I could be wrong. Glider pilots do not need licences and gliders do not need CAA CofA hence don't have to do some things that power flyers/planes do.
You can always either buy your own copy of Laws and Rules, or read the ANO/RotA from cover to cover, and quote them to show your own erudition in future!
Shortstripper, your experience in the 1980's that air law exams had to be passed before going solo in gliders was not typical. Formal exams have to be passed for Bronze, not solo. It is the practice to ensure that certain rules of the air are known before solo - e.g. rights of way for conflicting traffic etc., but orally not written.