I have no idea how they calculate this, but interesting nonetheless.
On a more useful note, I linked on the side bar to a forums post Oxylos did a while back on healing as a restoration druid. Incredibly useful and insightful post for us trees. I mentioned in my introduction post that I wouldn't be doing any complicated spirit vs intellect calculations (too much math for me). Plus Phaelia at Resto4life has already done these amazing posts! See her latest one on +MP5 vs +Healing here.
Just when I think I know something about healing, posts like these make me realize I have a loooong ways to go.