Also, statistically, factually, theoretically and in practice, you are wrong about higher percentages bringing you the proof you speak of. It's impossible to claim that it definitely means more people raid.
It could mean that instances are easier.
It could mean that people have become more skillful
It could mean that more people raid
It could mean that people that left weren't raiders.
It could mean that dungeons that wouldn't count as raids suddenly do count as raids and therefore their statistics add up.
Whichever it is, it does not mean that all people that didn't clear endgame content, aren't raiders. It also doesn't mean that classic content had less raiders. It could, but that's what I talked about earlier, it's how you decide to explain those statistics. I swear, hands down, that the only reason that 20% could be obtained, is due to the fact that LFR and normal modes are easy to complete for the bad people out there.