Isn't a lot of Ulduar's hype and longivity from open to Yogg-0 because its the first raid with an actual hard mode; I mean the mind set of we are creating fight A and Fight B and fight B will be harder on purpose? Until that point all fights had been Fight A, and they gated them with what Blizz in house would think to be "unkillable until nerfed fights' Cthun, M'uru (proved wrong because folks did beat it) etc being a few examples that come to mind. Raiders had never actually been tested at the level they were in Ulduar Hmode until then. Also, wasn't Yogg-0 a fight they tuned in a nearly unbeatable fashion, wasn't it nerfed soon after the kill. This is all off the cuff memory.
ToC was the first raid to be built in the idea of rushing expansions. Could we get away with a raid that is essentially one room. Soon followed by Rub Sanctum that taught blizz okay, maybe we actually have to make the dragon relevant and the raid worthwhile. Wrath isn't a good measuring stick for things, Wrath was a huge test bed as an expansion compared two the prior to and the ones to follow. Cata is the more formulated expansion really. Yes, it was a fail but I think its the true ground work for wow expansions. 3 raids, 5 patches, mild gating and then new expansion. I feel 5.3 being a large lore patch, bigger than what we saw with 5.2. But only time will tell.