EDIT: (Never mind, that was exactly your point :P)
The percentages Blizzard uses are just for show anyway. "20% cleared DS, it's a success!". They are not going to give us exact numbers all the time because that could just create negative publicity. And still, numbers are not everything. 80% can set foot into LFR but that doesn't mean all those people liked it or not.
---------- Post added 2012-10-04 at 02:16 PM ----------
There is no real definition of a WoW raider. I would say someone who does an attempt at a raid (not go in and out) regularly is a raider.