Power Attack is weird. Instead of using your weapon attribute, it uses your Strength attribute instead to calculate your weapon damage. Your weapon attribute is only used to calculate if you get regular damage if you meet the requirement, or start weapon damage if you don't meet it.* So you'd need 12 Strength to deal 100% damage with your weapon, but then you also get the Strength armor penetration bonus as well as the Power Attack +damage bonus.
*Well, maybe the weapon attribute is used to determine criticals also, but right now I don't feel like testing.
Your explanation turns wrong for a ranger having 16 Expertise, 0 Marksmanship and dealing up to 44dmg with Point Blank Shot (+26dmg, Expertise based bow attack skill).
I started a discussion related to it at http://www.guildwarsguru.com/forum/s...d.php?t=129091
Actually, ran some more tests and Power Attack actually still uses the base weapon requirement and your weapon attribute to calculate whether or not it does its regular damage or starter level damage. The percentage of damage that you do is still calculated by your Strength attribute; I'll write up the equation later.
At any rate, Power Attack is different than most other attacks. In fact, it seems Point Blank Shot follows the same rules as Power Attack, possibly having to do with the fact that they're based in different attributes (Expertise and Strength, respectively) than the normal damage-dealing attributes (Marksmanship and the Warrior weapon attributes). I'm going to test some more of the Strength-based skills and see if they're affected the same way.
EDIT: Had some fun with the Master of Healing. For damage calculations, aside from first checking if you meet the requirement for base damage, it uses whatever attribute that attack is in. So for Strength- and Expertise-based skills, their damage calculations are done using Strength and Expertise rather than weapon attributes and Marksmanship. So in Ensign's guide:
This skill is awesome for W/Mo IDS runs... btw.. the farming build is this-
Str.-16(use sup rune and have a helmet that gives +1)
Swordsmanship-13(use sup rune) BTW...must have 15pt att. quest!(both)
healing prayers-8
and the rest on tactics
Skills: mending, live vicariously, balthazar's spirit, watch yourself, power attack, dolyak signet, spring, and defy pain