According to WoWProgress.com we have very roughly, 50,000 guilds that have cleared 8/8 to 1/8 heroic. That means the bottom part was mediocre but they stepped in the thing and tried it (more than just wiping on a couple of bosses). Multiplying that by 17 which is roughly between 10 and 25 we get around 1,000,000 players. This is generous because people often say 10mans have taken over lately. However, accounting for guild hopping making the actual guilds less and the fact I excluded everything below top 50,000, that may compensate about the '17' generosity.
So, if we assume that this rough and questionable estimation of 1,000,000 players is correct we can see that actual normal and heroic raiders are a minority. It makes sense therefore to not be the last word on what is happening in the game.