Colin, I don't know if they have similar privileges in Canada, but there are 
regulations governing free matter for the blind which are available from 
most post offices.  I even remember reading them in Talkingbook Topics back 
in the 60's.  But just because someone mails something free matter doesn't 
mean they aren't abusing it.  At one time it only applied to talkingbooks 
and other such devices, but it was extended to letters later on which was 
probably a mistake.  I even know of a sighted person who tried to mail taped 
letters free matter even though the regs specifically said that a sighted 
person is not entitled to those privileges even if the correspondence is in 
Braille, on tape or in any other accessible format.  But people abuse things 
which is why we end up losing them.
Harvey