The tank stages on Maintankadin may vary a bit in implementation, but they're based on the same assumption. The differences are mainly a matter of granularity and viewpoint concerning the breaking points.
I'll give my view of the different stages, based on a higher granularity than I use myself.
1) Newly dinged 85. This happens the moment you become 85. Theoreticaly all the best gear in the game are available for you from this point on. In reality you are clad in a hopeless mix of gear suitable for questing and levelling. Most of what you have should be a wild mix of 312 greens to 325 blues.
2) Prepared to start your career as a max level tank. This ought to take you a day or two. If you've levelled an alt it could also be a matter of a few hours. You'll run the initial Molten Front quests to unlock the vendor Zen'Vorka and gain access to a couple of ilevel 365 taking items. You also do the Thrall quest chain to get the tanking cloak. Depending on your stash of gold you should visit the AH to shop a few upgrades.
You are now ready to tackle all level 85 five man dungeons on normal difficulty.
3) Prepared to tank hc. This really means that you have amassed the gear needed to tank the first Cataclysm five man heroics, no matter which one chance gives you when you try your luck in the LFD. You have spent a few more days, maybe a week, doing daily quests and tanking normal difficulty dungeons. During this time you should have gained a few ilevel 333 blue items as well as ranking up your reputation with the zone-factions by means of tanking dungeons with a faction tabard.
You are now mainly geared in ilevel 325 and 333 blue items. This set is boosted by three or four 365 items. In all likelyhood you have also bought a couple of ilevel 353 items on the AH as these costs only a few hundred golds. Almost all your gear ought to be properly gemmed and enchanted, albeit with second best in slot gems and enchants unless it's the 365 slots.
4) Prepared to tank the Troll instances. You have spent a week or two learning how to tank when things make a serious attempt att killing you. Running Cataclysm first tier heroics should see you having access to the best shoulder and head enchants in the game as well as getting you the reputation needed to collect a few ilevel 359 gear. While you might still be saddled with a single green quality item you should prepare to get your head smashed in by the trolls.
You are now mainly geared in 346 blue quality items, but your gear is boosted by six or seven slots of ilevel 353 or better quality.
5) Prepared to pug Cataclysm first tier raids. Basically this was true the moment you were ready to take on the troll heroics, but verbal abuse when you tried your hand at the previous tier of raiding content should have forced you to clear up some more slots. This, in all likely hood, is the result of gaining a few drops from the trolls as well as unlocking the vendors from the Molten Front. You shouldn't have to spend more than a few days at this stage.
You are now mainly geared in 353 and 365 epic quality gear. You also have access to one, or possibly two, ilevel 378 items due to collecting valor points. By now you are in reality hysterically overgeared for pugging the initial raids, but at the other hand it's a way to learn the ropes.
6) Prepared to raid. Unless you joined a raiding guild, the previous stage sunk you into a quagmire, and you have easily spent a month pugging for little gain. The problem here is that albeit you are geared for raiding the current content you're unlikely to do so without a guild. Still, 980 valor points weekly and quite a few pugged easy mode raids should have you prepared for harder content.
You are now mainly geared in 359 and 365 epic quality gear. Four slots are of ilevel 378 epic quality, and you are in reality well overdue to tank the Firelands raids at normal difficulty. This is most likely your end-game.
7) Hard mode raider. You got yourself into a guild and have had your arse handed to you in the Firelands raids. However, reputation gained there as well as maybe a drop or two should have you geared to fail miserably when one of the usual tanks don't show up at raiding time. You'll either revert back to a stage 6) tank, or you'll spend most of your free time developing the skills needed to handle content that truly is out to get you.
You're now mainly geared in 365 and 378 epic quality gear. The ilevel 391 gear beckons.
8) Trailblazer. You've killed it all. WoW starts again when the next content is available on the Public Test Realms. Everything is farm.
You're balancing your 391 gear against the lower ilevel slots which in reality are an upgrade depending on which boss you're planning to pull. You're not reading this blog, because 'casual' is about the least proper word to describe you.
Now, we can't have eight tanking stages when we make gear lists. We have settled for five, and that is likely one too many. However, settling for a lower granularity means cutting corners, and that's the reason you see different numbers sharing the same piece of gear. Also, totally unaccounted for is the knowledge among us gear-list makers that a simple rank is very seldom entirely true.
Some fights require extra health, some that you take as little damage as possible when it counts, and some that you simply take as little damage as possible. Where one fight has you scrambling to get that magic 102.4, another might see you stacking stamina like there was no tomorrow. In reality we can't afford, mostly as a result of time (the raid won't wait for us to regem and re-enchant), to be perfectly configured for each fight. So we make gear sets, and those gear sets have no stage ranking. They're simply an assortment of gear available to us to do the best job at the moment.