The issue here is not actually the use of an apostrophe, but the use of the whole 'S (apostrophe-ess) suffix. The 'S suffix indicates possessive, e.g. "John's house" = the house possessed by, or associated with, John. But there are cases where the whole 'S suffix can be omitted, and one of these is when the noun is a group. "The board chairman" ~= "The board's chairman"