When I see an awesome drama that is beyond every drama I've ever seen (exept a few), I tend to feel like rating it 11...but since there is no 11, I re-rate all my dramas to keep at 10 only the dramas I judge on the same level as that special one I've seen. That's why you can see a lot of 5-6-7-8-9 in my list (I even have a few 4-3-2-and even a 1)
By the way, I think that it was nice in this new version to call "Masterpiece" for the 10 rated drama.
I like the message it send : "Rate 10 only the drama you consider a masterpiece, a true work of art that should be put in the history books of all dramas of all times. If a drama is awesome, but doesn't seem like deserving its place in the drama Pantheon, just rate 9, it won't hurt it."