An example of this is the fact that elemental and restoration, a damage spec and a healing spec, share spell power mail which is usually far better itemized for restoration than elemental. Meanwhile, elemental is a pure spell casting damage spec, and enhancement is a hybrid spell and melee damage spec, but they share absolutely no gear and when it looked for a while that enhancement would actually benefit from a caster weapon and perhaps a few other caster pieces steps were taken to ensure that enhancement would no longer benefit from caster gear. Instead, again enhancement was steered towards hunter mail and slow/slow main and offhand weapons with no caster specs on them.
Patch 3.1 really showed us the consequences of gear consolidation on a class as hybrid as a shaman. Since shamans don't use various forms to access their abilities like druids do, there's no inherent limiting factor preventing variant specs from utilizing each other's gear. A tree druid in tree form isn't going to gain anything from trying to cast damaging spells, but if there was a fluke talent in restoration that granted some ridiculously high spell power that made restoration shamans in elemental gear capable of doing as much or more damage as elemental shamans (while still maintaining their ability to heal as restoration shamans) it would be much more immediately apparent. One is reminded of the very odd strategy my guild used a few times on hard mode Vezax 10 kills of having my shaman spec enhancement, wear elemental gear, and use Maelstrom Weapon procs to heal the tank while regenerating mana with Shamanistic Rage. (I used a fast caster weapon enchanted with Everliving for this, as DPS wasn't really the point.) It's not the intended use of the spec or the gear, but it works. (Well, worked, I'm fairly sure they hotfixed the encounter so that this isn't viable anymore, but I haven't done it in months now.)
This also leads to issues like elemental shamans persistent lack of proper scaling. This isn't itemization's fault by itself, but again a consequence of how itemization interacts with talents and class design. Unlike other casters or caster/healer hybrids, elemental shamans gain practically nothing from spirit. Furthermore, there's no talent for elemental shamans similar to Mental Quickness, which grants additional spell power as a percentage of attack power. (This ability is what allows enhancement to do meaningful spell damage without wearing spell power gear.) While there's no reason for elemental shamans to want a talent that converts attack power, the fact remains that Mental Quickness scales an enhancement shaman's spell damage with the gear he or she wears in a direct and meaningful way. Since elemental has no talents that boost spell damage or spell power based on an ascending stat (spirit or intellect for most other caster classes) it simply does not scale as effectively as those classes do.
The existence of Shamanism was an attempt to redress this without directly mimicking other classes' abilities like Fel Armor. Since Shamans are disinclined to stack any spirit (despite the fact that spirit is a shaman's highest baseline stat, the class gets little to no benefit from the stat) you could certainly make a reasoned argument that a talent that made use of spirit would be useless in the current scheme of itemization... it could even drive shamans towards leather and cloth items instead of away from them, which certainly seems to be the current goal. It seems likely that the lack of spirit on mail combines with the design of shamans to be averse to spirit, and that the scaling issues introduced by this decision (and combated by talents like Shamanism) are an inherent consequence of designing a mail wearing caster hybrid and trying to keep it in mail.
In the end, the up side of shaman class design (a class that can fill a melee DPS, caster DPS and healing role) is also the dark side, the pure hybridization makes itemization always tricky, especially in the era of gear consolidation where you don't want to have a piece of armor drop that is purely designed for one spec of one class. If your design goal is to avoid drops being sharded because only one spec can possibly make any use of them (holy plate ahem cough cough) then talents need to step in and fill the gaps left by such broad gearing. Elemental shaman scaling is, to some degree, the unfortunate victim of this design goal.
Next week, I'm hoping for a special surprise column discussing shaman issues with a special shaman think tank. However, if things develop apace, it's possible there will be a gear list here for 3.3 instead.
Check out more strategies, tips and leveling guides for Shamans in Matthew Rossi's weekly class column: Totem Talk.