From the Nov 25 2010 Patch Notes

The following adjustments have been made to loot.
High quality +1 and +2 materials can no longer be obtained through combat. The frequency of drops will remain the same, though all items will now be either normal quality or high quality +3.

Prior to Version Update 　 After Version Update
Normal Quality → Normal Quality
High Quality +1 → Normal Quality
High Quality +2 → High Quality +3
High Quality +3 → High Quality +3
The change to battle drops didn't keep the +3 drop rate the same, it increased it (effectively a stealth nerf to gathering). I was very surprised that the exact same action wasn't taken for gathering drops.