While I think the answer deserves at least an article or two written about it, I'd say yes, tier 9 has developed into the new standard of gear upon which everyone is judged off of. I know that from a mechanical perspective tier 9 is far from necessary to run everything but Icecrown Citadel, and is most certainly not necessary for heroics. Yet when I go into a heroic and see a tank with less than 40,000 HP, part of me sighs and wishes for a new one, even though a 30,000 HP tank is going to do just fine.
The standard is irrational, and doesn't really do WoW any good. But nonetheless, it's something people have to deal with. One way to deal with it is to get your tier 9 shoulders as quickly as possible, those 30 badges are pretty easy to obtain. Once you've gotten them people will just look at you briefly and say "oh, tier 9 shoulders, good to go." Of course if they're using something like gear score (which is equally ridiculous as any tier 9 standard), then they might see otherwise.
The other thing to remember is that when people complain, just ignore them. If you're doing 1500 DPS in a heroic, then you're ready for the heroic. If you're not, then take a look at your rotation and spend some time on the practice dummy. If you still can't hit 1500 DPS, take a look at your gear and see what's missing. I've been able to pull 1500 DPS using level 70 Black Temple / Sunwell / Archimonde gear, so it's not too hard to hit. If you do need some gear, check the AH for a couple BoE level 80 blues and epics, and don't forget to roll need on any blues from heroics that can help you. Then when people complain that you're not in tier 9, you can just say "Since when do heroics require more than 1500 DPS?"
People will usually stop complaining after that.
Finally, remember too that this won't be an issue in six months or so when Cataclysm is out.
"What's the defense cap?"
Defense has a soft cap of 540. It's "soft" because defense still is useful after 540, just not an absolute necessary. If you don't have 540 defense though, you'll get yourself crit by raid boss mobs, and that's no fun. It's pretty easy to get these days with tier 9 gear, so it shouldn't be as big of an issues as it once was. The defense soft cap really don't apply for druids either, since they're talented into being uncritable.
"When is Cataclysm going to release? Do you have any leaks?"
We know that Cataclysm is going to release in 2010, but not any specific time-frame therein. In other words, we do not know an exact date. Sites like Amazon are not listing the correct date, the just list something so they can get you to pre-order the game. When the release date is finally leaked or announced, trust me, you'll hear it here right away.
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