It's a mix of things...
Against Higher Level opponents in PvE -- there's two things working against you:
- Their massive armour level and higher XP level
- Strength only applying to skills
We'll compare Dismember to Eviscerate at 12 Axe Mastery with 10 in Strength fighting level 25+ opponents
Dismember reads: If this attack hits you inflict a Deep Wound on the foe for 21 seconds
Eviscerate reads: If this attack hits you inflict a Deep Wound and strike for +34 damage
Now Dismember will hit for your base damage on an Axe (6-28) with 10% Penetration -- hitting for something low like 6-15 damage.
Eviscerate will hit for (6-28 + 34) with 10% Penetration -- the difference is we'll likely hit in the 35-50 region
In short, you'll see higher numbers on the +damage skills since most of the base Axe damage is absorbed by their high armour level. You'll also land fewer "critical hits" ( bonus damage ) against higher level opponents -- whilst they'll land more on you.
This really is why PvE becomes completely boring to Melee classes
I'll link to the Combat Mechanics guide -- http://www.guildwarsguru.com/content...nics-id674.php