Why do you need 100% correct data to gather a general impression? It's a game, not brain surgery, you don't need 100% accuracy. It doesn't matter if the % is 25% or 30% or 35%, just like it doesn't matter if its 1% or 2% or 3%. Statistics always work with a margin of error, that's why they are statistics. Sure there might be some really strange raiding guilds out there that dont use things like world of logs and wowprogress, but they are pretty rare, so why judging general tendencies based on exceptions?There is no real % at all when it comes to website and data all of these stuff are just theories and statistics they are never 100% true. do they help with gathering data and info? yes of course but do they prove and determint as a absolute fact? no sorry.
Honestly, for me this just looks like a commercial decision. Blizzard doesn't usually dish out un-necessary new content, they are more known for reshashing/reusing stuff. The only significant segment of players that will gain a lot from this are the LFR players - that are done and over-done with the content they can run. I assume they make a large part of the subs, so they need to be fed a new LFR tier, since normal/hc raiders always have something to progress on (unless they are in the 1% in the world that are done). Coupled with the sales for the wow games collection, it makes sense that end semester numbers need to be boosted. It's got nothing to do with keeping promises, they promised they will never make content for 1% of the player base again, and many other things.