Your character sheet rounds down haste and doesn't display fractional haste. (Which is kind of stupid.)
Perhaps I misunderstand something, but at lvl 74 227 haste rating converts to exactly 10% haste on my character sheet. Using your table, that would match the expected value at lvl 75. What am I missing?
You do however get the full haste, even though the sheet rounds down.
At 74 with 227 haste, the table says you'd have 227/21.134... = 10.74098... % haste.
Is your Drain Soul 15s/1.1074098 = 13.545s cast time (spell book should round up to 13.55s)?
If it is, then you have the full 10.74098% haste and the table is correct.
If you hit 75 with the same gear, you should have 227/22.739... = 9.9828% haste.
The character sheet should then display 9% and Drain Soul should be 15/1.09828 = 13.5677s cast time (spell book should round to 13.57s).
If that's true as well it confirms the table.
Also, what's up with people complaining about the increase of stats/rating needed?
Let's take a simple model:
* At 70 in some blues you have 1k AP and a 70 DPS weapon. About 140 character pane DPS.
To increase that by 1%, you'd need 19 AP or 1% hit.
* At 80 in some blues you have perhaps 2k AP and a 120 DPS weapon, around 260 character pane DPS.
To increase that by 1%, you'd need 37 AP or 1% hit.
37 AP at 80 costs about twice as much as 19 AP at 70. That's why 1% hit at 80 has to cost about twice as much as 1% hit at 70.
The model is simple, but it shows the basic thing about scaling. Doubling the ratings/stats needed looks pretty natural.