Sometimes these contain new features, but just as often they simply fix existing bugs.
No, the word simply does not apply to the games you mentioned. Real-Time Strategy and Multiplayer Online Games, unless they are played competitively, tend not to have levels, stats, or other things that make people feel that they have to "grind" through a portion of the game. For example, you do not have to chop down X-number of trees or shoot Y-number of terrorists in Counter Strike before you unlock a skill or skills - unlike some MMOs.