I like this guy in the original post because he knows what to look. He could have suggested thiefs blade.
SF actually has 33/37 low end damage and 59/63 highend damage because of the +4-8 shadow damage, this is of course factored into the DPS. DPS isn't the ONLY thing to consider in PVP because you also have to look at highend damage which gives more burst potential, this is a reason [item]Gutterblade[/item] sucks because the highend damage is not good
Shadowfang also has a 30 shadow damage proc that can crit if you have any crit rating gear or skinning. Previously twinks only had int for spell crit and agility for melee crit. Crit rating provides both which is why fiery weapon and this shadow proc are criting more often these days.
Cruel Barb has 57 highend damage and 12 AP which is far more than the 4AP that butchers gives.