Armour is also included in this rule. Therefore Heroes (and Henchmen) that do not have a particular type of armour (whether it is Heavy Armour or Shields) cannot use that type of armour and there is no skill to allow the use of armour not listed in the warband equipment list.
For the purposes of this rule, Gromril Armour and Ithilmar Armour are treated as Heavy Armour (they are just Heavy Armour made out of a different type of material similar to the way that a Gromril Axe or an Ithilmar Axe is still an Axe but made out of different materials).
I suppose that a Pavise would either be treated as a Shield in this instance or else is actually equipment (otherwise no
warband would be able to use Pavises!!).
Toughened Leathers are actually equipment that counts as armour so it can
purchased by any Hero (not Henchmen though unless it is in the warband equipment list for the Henchmen group) but still cannot be worn by spellcasters like proper armour.
If you do searches on this forum (and maybe the SG forum) then you will find the threads to back up what I have said above except possibly for Pavises which I just thought of now and do not recall reading about anywhere else.