Pre-TBC dungeons never really had strategies.
There were always certain moves to watch for, but basically you CCd and stalled and spread out damage intake and just figured a way through it, and sometimes it just came down to gear and group comp. Now the gear, spells, and overall stats of players makes bulldozing these zones insanely easy.
TBC Heroics (70ish) were really the first place that sincere strategy was needed, at least for a select few bosses. But as gear and spells have progressed these dungeons have become mind-numbingly easy as well.
It was not long ago that, in bad gear, some of the Wrath Regulars were somewhat difficult and required some form of strategy. In fact, Nexus has a strategy for every boss and it's one of the first dungeons for Wrath. It was also not uncommon to do Nexus in 90% TBC gear, meaning stats were low so death came quick. With good gear, though, most strategies can again be forgone with straight bulldozing. A lot of this will also depend on your abilities to heal through TARDS (Totally Avoidable Raid Damage Sources). The term will start to take on other meanings at this point, though... The back end up Wrath was always easier because the gear from questing and doing other dungeons catches you up to that playing field.
Then comes Cataclysm. A cycle similar to Wrath occurs: in the first stages of doing these dungeons, the fact that you do not have full cata-level gear makes them more difficult. As you progress through Cataclysm the dungeons get easier and easier, but still require strategy. Once you hit 85 your coefficients hit a brick wall and all of a sudden your mana regen is crap as well as all your other ratings and stats. The cycle goes through once more: starting out harder and getting easier.
A good 70% of bosses in Cataclysm heroics have an instant-kill ability. A strict definition of strategy is a bit of an overstatement on what is required for trash pulls, but certainly basic RPG strategies including Focus Fire to get Damage Intake lower, Controlling/Killing healers, avoiding Area Damage, etc all come into play. As gear progresses, especially in the DPS department, the requirement to strategize again drops. It then becomes simply a "don't get 1-shotted" game.
Firelands, the new Raid Tier, forgoes the 1-shot mentality for the first time in Cata. It's more of a slow-burn effect that messing up now will cause your healers to run OOM further down the road, and the fights are so long that DPS cannot help adjust this. This is one of the only places you'll find true strategy required. ZA/ZG offer the opportunity to use Strategy to excel, but again do not require it depending on gear.
Another really great place to apply strategy in this game is going to be PVP. Arenas offer a great place to pre-define routines for you an a partner(s) to use, where Battle Grounds (especially RBG) allow you to really put full-scale logistical strategies to work.
Edited, Jul 31st 2011 3:03pm by tzsjynx