Nope, they're not :-)

Actually, what the screenshot best demonstrates is actually how unreliable short term DPS numbers are because of crits. You have nearly identically geared elemental shammies and their DPS on a single boss fight ranges from 2200 to 4000 (!). Presumably they were all spam casting and no-one was out of the fight (hard to imagine anyone but the tank getting snake wrapped if you know this fight). I guess some of the variation might be due to heals depending on how you macros are set up, though I don't need to heal at all on Slad'ran anymore myself.

This drives me crazy about the target dummies as well, identically geared or repeat runs see a variation of up to 10-20% in DPS numbers due to variability in crits. Very hard to tune your macros/gear when RNG dependent crits have a much bigger impact than most minor (e.g. single slot) changes.