Pyro,
We use haste %'s because it's the same for everyone. For example, let's say you're a Resto Shaman. All resto shamans want to get to 25% Haste (let's say). That's the same no matter your race or talents. But, if you have Ancestral Swiftness AND you're a goblin, you need 5,199 Haste Rating on your gear. If you aren't a goblin, you need 5,676. If you are a goblin but don't have Ancestral swiftness you need 7,584. And if you're not a goblin and don't have Ancestral Swiftness you need 8,085. All of those numbers still get you to 25%.
However, theorycrafters haven't adopted the % yet, and tend to only talk about the haste rating. That makes it really hard for people who want to put those haste ratings into our site. For now, if you scroll to the end of this
article, you'll see a haste rating calculator right above the breakpoint image. You'll want to put 0.126 into AMR.
But one more thing! We're always looking to improve. We know that a lot of people like haste ratings! So we're working on a super-fancy feature that let's you pick your breakpoint. The big idea we have is that it will also show you what you get at each breakpoint to help you choose the one that's right for you