Your profession and race -- in RMSS -- may define certain skills as Restricted, Everyman, or Occupational. If you pay the DP for one rank in an Everyman skill, you receive two ranks. If you pay for one rank in an Occupational skill, you get three. Restricted skills, on the other hand, require you to pay for 2 ranks to get 1.
So, Everyman skills may be developed more cheaply and more ranks per level than regular skills, and Occupational skills even more so. Sometimes the system will give those boosts when a single skill should be easy for you to learn (e.g. animists and herb lore) rather than decreasing the cost of the entire category.
There was an early printing of RMSR in which those three classifications changed the skill costs rather than working as I just described. I think Markc is referring to that regarding the different printings. But I am pretty sure by the second printing and all subsequent printings it worked as I just stated.