The original concept was not my idea. I merely adopted it from Dragontamer, and it was his method of analyzing defensive capabilities. However, regarding the use of the algorithm of 1.1, I'd assume its so you can make a rough estimate as to the difference in damage resistance. A Pokemon with 121.0 Defense as an example, will take 10% more damage than one with 122.0 Defense.
Hi Ulevo, just checked out your defense tiers cause im a nerd and thats interesting to me :) So I was wondering why exactly you take base log of 1.1 after multiplying HP and Defense. It seems much easier to comprehend the whole number- say 400 HP and 300 defense gives you 120,000 defensive rating. Mainly, no defense Blissey to max defense going from about 110 to 119 in these ratings doesn't make it immediately obvious that its physical capability is more than doubling. Im sure there's a really good reason, just wondering.