I find this interesting because it's illustrative of the complexity of the game itself and also of the elemental shaman and the way the class interacts with others for its damage potential. We can assume that the damage loss moving from Naxxramas to Ulduar is real, because the developers are already hotfixing a change to compensate for it (something they have not done for other classes that have demonstrated DPS loss in Ulduar) and so we're left with something of a mystery. Why is elemental shaman DPS decreasing since patch 3.1?
I won't pretend I know better than anyone else. If the people who work to predict and design these systems didn't see this one coming, and it's not due to an obvious nerf (which it's not) then it baffles me. But we can still muse about possible culprits. (By we, I really mean we here. I want to see what you guys think, because I have to admit, I cannot figure this out. I've looked at raid WWS for my guild and our elemental shaman does seem to be lower, but he and I discussed it and he has no more of a clue than I do. Since all my gear is resto, I offspec elemental but am by no means an expert yet.)
One candidate that was proposed was that elemental hasn't changed, but that other DPS (like rogues and feral druids) simply improved. While it's true that several classes are dominating DPS in this patch, I don't think we can really place the blame here. It's one thing to notice other people are out-DPSing you more than previously, but that wouldn't create the belief (which again is backed up by Blizzard's own change to the class) that elemental shaman dps is decreasing. Instead, you'd see "My DPS doesn't match up to X" posts. While the power of perception is indeed capable of influencing people's beliefs without relation to what is really happening, it would have to be a huge shift for people to feel they were actually losing DPS, not merely failing to progress as much as others. It's plausible, but not very compelling.
Another possibility is in the nature of the fights in Ulduar. This ignores i started to get better gear from Ulduar and i hit for less on same mobs with same buffs but we'll consider it for now. Is it merely the nature of fights in the new raid, which call for more mobility than Naxx? I don't know that I buy this. Sure, there are several fights in Ulduar with mobility concerns (Iron Council, Ignis, Kologarn with the eyebeams and being grabbed, Mimiron with the Leviathan-style Barrage to name just a few) but elemental shamans are hardly the only ranged casters with cast times to consider in fights like these. Being at range, you'd expect less interruption for them than, say, a paladin or warrior. We can't discount the nature of Ulduar fights but we also can't consider it a case closed for the mystery, either.
Losing 5% crit from Improved Scorch strikes me as the least likely option. Frankly, elemental shamans don't really need to worry about crit as much as other crit dependent casters, because it it's really important to crit they can jack up their critical strike chance with Elemental Mastery or force a crit with a Flame Shock/Lava Burst combination. It's not impossible that the Improved Scorch change is to blame here, but if it was, why wouldn't it affect other casters in the same way? Elemental shamans are hardly the only DPS casters who like to crit. GC himself notes that boomkin and warlocks who also rely on crit to some extent didn't see any recent downturn, so to me Improved Scorch serves more as a red herring for elemental shaman DPS downturn than an actual suspect.
What about gear? Is gear the issue here? Our original poster mentioned that her DPS decreased once she began accumulating better gear from Ulduar. Is the culprit a loss of set bonuses? Without knowing what pieces of Ulduar gear have been equipped (an armory search for the OP's name didn't turn up much at the time of posting) we can at least look back to our discussion of Ulduar set gear for shamans. especially our comparison of the various tier 7 and 8 sets, we can see that the Worldbreaker set in no way loses you anything you'd want as an elemental shaman. And looking at non set gear, this comparison of an Ulduar 10 chestplate with our Naxx 25 elemental set piece shows that you'd certainly not expect a huge loss for equipping it. Losing 3 crit rating and 2 sockets for 10 int, 24 haste and 10 spell power seems like a very fair trade. It's even more so when you include this 25 man elemental BP into the mix. (I admit now that it's not entirely a fair comparison, as that's a Yogg-Saron drop, but it's not a hard mode drop, and Yogg is difficult but certainly killable as many guilds are in the process of discovering.) So while a loss of set bonuses might explain some of the DPS drain, the gear itself certainly seems set up to contribute DPS, not penalize you for it.
Perhaps it's all of these reasons contributing at once. The crit loss from Improved Scorch, changing itemization, new fight mechanics, and other classes seeing dramatic improvement combine in a perfect storm of dps issues for elemental. None of them able to explain the overall dip by themselves or even able to cause much of a change, but like the fall of a leaf in chaos theory the path becomes harder and harder to predict as each new variable is introduced. Would this be self correcting? It's impossible to say, but clearly since a buff has already been hotfixed into the game it seems that at least someone at Blizzard doesn't think so. Will a 13% increase in the chance of Lightning Overload procs be enough, too much, or just right like the last bowl of porridge a golden haired little girl stole from innocent, sleepy bears? Is this a minor course correction or will we end up seeing elemental DPS inflate once whatever mystery condition is at work ceases?
I'm not terribly worried about that, because I expect even with this change elemental DPS will be solidly in the middle of the casters, neither lowest nor highest. I won't pretend I wouldn't rather be underestimating it, but we'll see what shakes out.