this

I've been to a few partial guild runs, where I was not part of the guild, where people insisted on destroying all four towers after talking to Brann because they didn't want to do the hard modes. I think the toggle mechanism is easier to understand.

They should have it more clearly communicated, but the Ulduar method is still superior to a drop-down menu.

A number of the Ulduar hard modes functioned as gear checks just to activate them -- if you can't activate Thorim hardmode, you don't have a chance of beating it. And yeah, having Sif there definitely integrates with the Storm Peaks story in a way that "OK, I clicked hardmode" would not.

Likewise, the more granular hard modes on Sarth, Freya, the Iron Council and Yogg-Saron are something I really enjoyed, where you can work your way up to the big rewards. A binary system is a huge step back.

Oh, and Flame Leviathan is granular, too. I think that's all of them ...

I agree. But we have to remember that Ulduar was designed that way. The activation of hard modes has some kind of lore/reason to it.

We don't know yet how are designed the final version of the ICC boss encounters. If they are somewhat near to the TOC ones (straightforward story, just kill the boss) then the new system applies perfectly, (maybe this is why they would change TOC, but not Naxx or Ulduar).