The system, called "progressive percentages," was cribbed directly from Blizzard's own Warcraft 3, which used it for critical hit mechanics. It relates to how and when quest items drop from creatures--an important issue to all WoW players. nope
Originally, Blizzard settled on a standard WoW quest item drop rate of around 35%, with no system in place that would tweak the percentage as players killed more enemies.
"We found that this had a lot of problems where players would run into streaks, and they only remembered the shitty streaks," said Kaplan. "So what we decided to do was we took a page out of Warcraft 3, which had a very elegant design which they referred to as 'progressive percentages.'"
In response to this frustration, the developers quietly rolled out a change to the system with last year's Wrath of the Lich King expansion.
"So what we did recently with Wrath of the Lich King, and it's something we've never really talked about before, but in Lich King, every creature that is part of the collection quest has the item 100% of the time," continued Kaplan. "But we do a progressive system where we up the chance the player [gets the item] each time he kills it."
The percentage at which an item drops can eventually reach up to 100%, or a guaranteed drop, according to Kaplan.
"The problem was, when we put it live in the beta--and we didn't tell anybody this--we found that while it was great that it got rid of the bad streaks, it also got rid of all the good streaks. And overall we needed to raise the base drop percentage to around 45%."