My gut instinct was, "Ugh, why are they nerfing everything so badly? That's ridiculous. Just because it's the end of the expansion doesn't mean they need to make it easy mode for us." Then I actually thought (gasp!) about it for a little bit. Looking at the changes coming in Patch 3.0.2, this was a change they needed to make to let us still raid until Wrath. A lot of encounters probably became impossible to beat as they were with those changes, Sunwell Plateau especially. Sunwell was designed with all of the insanely OP stuff players were doing to win in mind. Stacking Shadow Priests for mana regen, stacking Shaman to chain-cast Heroism/Bloodlust, half the raid going Leatherworking for Drums, yadda yadda.
Those are all things they nixed for Wrath of the Lich King. Lots of Shadow Priests and Heroisms were more or less mandatory to progress through Sunwell. With mana regen from Shadow Priests nerfed, your Caster DPS would never, ever last through half of the Sunwell encounters, even chaining mana potions. Their personal regen is quite simply not enough to beat those encounters as they are. Sure, some of your casters can just stack more MP5, but if they all did that, you would never make the DPS check. The boss would enrage and destroy you all. Every single time.
It's the same with Heroisms. The DPS checks are built with the assumption that your raid is stacking Shaman, simply because they're available to you. If they didn't design the encounters with that in mind, they would be too easy. Your raid would bring 6 Shaman and /rofl through the entire zone. It would trivialize the entire place if they didn't plan for that. Is it lame? Yeah, but it was necessary. With Wrath and patch 3.0.2, you can't chain them anymore, so they needed to fix old content to compensate. You simply would not be able to meet the DPS checks with only one or two Bloodlusts.
So this wasn't a needless nerf to the zones so much as an absolutely necessary retuning. I'm very glad they did it, because it means we can actually continue raiding if we want to. You can make that final push to Illidan or Kil'jaeden or whatever you're working on without being totally screwed by the patch.
I wouldn't be surprise if they made a lot of other changes we haven't seen yet. Bosses not hitting as hard to compensate for some mechanic changes, Crushing Blows being retroactively removed from everything, et cetera. We'll see what else crops up, but I have a feeling less HP across the board isn't all we'll see.