The thing that dismays me the most is this concept that every single monster has to be stacked against the archetypical party, and that it's fundamentally flawed if somehow thats not the case.
For the MM1, that was for the best. New system, new rules, little third-party support as yet, you needed to make the first source of opponents as broadly applicable as possible.
Six years down the line, though, and that's not the case. Many people want to play games that twiddle with the fundamental assumptions -- lower magic, less reliance on items, gestalt, whatever. And with the proliferation of base classes, you're starting to see more parties outside the ftr/rog/wiz/clr paradigm. An original ogre-mage might not be able to go toe-to-toe with a ftr-bar duo, but what if your group consists of a beguiler, druid, cleric, and duskblade?
Another thing that irks me is the assertion that once you have a critter that fills a particular niche, that creating something else that overlaps is pointless. I don't know about you, but most players have killed legions of orcs, ogres, skeletons and zombies. Something that is mechanically similar (not identical) but very different in flavor is something that a lot of people welcome. It keeps the experienced players a little on their toes, and gives more options for DMs that want to run something other than the Realms or Eberon.