It's quite difficult to accurately measure the number of players that were sitting on high ratings during season 11, this is because it was the last one for Cataclysm and a large number of players were idling in anticipation for Mists of Pandaria. Generally, it is quite rare for us to see large numbers of players that will achieve a high rating and sit there successfully without playing for long periods.
You have to play a certain amount of games a month or whatever across the whole season till the end to be eligible for titles. If you don´t play your rating drops.
This is something that is always under discussion. Rewarding people for not playing is something that we don't like. No matter the rating system that we use it is still going to cause players to try and play the system and not the game itself. This is something we would like to avoid and the reason that it is still heavily under discussion for us.