Tier = ilevel

Vanilla:
T0 = 57-63
ZG = 65
T0.5 = 66
T1 = 66
T2 = 76
AQ = 78-88
T3 = 86-92

BC:
T4 = 120
T5 = 133
T6 = 146-154

WotLK:
T7 = 200-213
T8 = 219-226
T9 = 232-258
T10 = 251-277

As you can see, between T6 and T7 we made a ~2-4tier jump from BC to WotLK based on item level, as opposed to the ~1-2 tier jump from Vanilla to BC.. As an above post stated.

Look at the massive jump in WotLK. I hope in cata this gets toned down a little

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Q u o t e:
He also said that they are just numbers. They aren't at a point where comprehension becomes difficult or mathematically taxing. 10,000 Spell Power would still just be 10,000 Spell Power.

The rapid inflation was a result of hard mode loot, which wasn't initially intended or planned for.

To tone it down, they aren't decreasing values.They are increasing health pools. You're still probably going to see raw numbers get larger and larger.

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Yeah, exponential power growth is just part of the design. It doesn't really bother us that the delta between character level and item level keeps growing. It might be a problem someday if it takes scientific notation to express how much Agility there is on your breastplate.

The problem folks are referring to for this expansion is that we based combat ratings, especially things like crit and hit, off of one assumption for what gear would look like in 4.3, but adding the hard modes meant that the gear ended up having more stats than we thought. If we ended up squeezing in additional tiers into Cataclysm the same thing would happen, though we also have some ideas to make the scaling work better in general.