I gotta agree too, its not that hard for the reputable sellers who car about what they're selling to add torque specs either on a piece of paper or even stamping it on the part if the part is large enough. I know Fred puts the torque spec on his site in the description and that's still better than nothing, but most others simply don't bother.
Especially for aluminum parts where a bolt is threaded directly into the aluminum, some specs should be listed to prevent overtorquing and stripping the threads. There are also torque tables online that tell the recommended torque range for bolts nuts and studs etc depending on the bolt size and grade, thread pitch, and material they are threading into. Anyone can look these up on their own but it would be common courtesy to include this with the part that's sent out.
The torque tables do come in handy when modifying our own parts as well because any change in material or bolt diameter or thread pitch so optimum specs can always be achieved but if we make or sell a part, this info should be included as well as other info like tightening sequence if needed, and whether or not a gap is required on one side or both sides on parts like these hub adapters etc.