Well at least you know where to look now. The ARB is an extension introduced before FBOs became core in 3.0. That's how most features are introduced into OpernGl, first as an extension then if there is popular support then it is added into the core profile.
The vast majority of the extension is exactly the same as the core just with ARB added on the end of names. A few things have different names but do the same thing. And a tiny few are added \removed.