My old man once told me "no matter how good you are at something there will always be someone around the corner doing it better so you must always do your best"
You really don't need complicated maths and statistics to reach the conclusion that,if the above holds true,with the size of the population in WoW there are many more people playing much better who are spread out among more guilds with the very best of players consolidated in many more than just the two or three guilds as is the case with Rift.