From the Star Wars D20 RPG: Dark Side Sourcebook
Renegade Jedi
Because the renegade Jedi were exiled from the Old Republic before the development of personal blaster technology, Sith of this period do not receive the feats Weapon Group Proficiency (blaster pistols) or Weapon Group Proficiency (vibro weapons); instead they receive the feats Armor Proficiency (light) and Armor Proficiency (medium), respectively.
Similarly, when these Jedi left the Old Republic, Jedi Knights armed themselves with ordinary swords. While the Old Republic developed lightsaber technology, the Sith empire explored alchemical metallurgy, resulting in the mystically honed Sith sword. Thus, Sith of this period cannot take the feat Exotic Weapon Proficiency (SIth sword) instead when it becomes available through their class abilities. (If Sith charactyers come across lightsaber technology