At one level, this is word-games. I wouldn't personally construct a sentence with "educability" in it very often, but I have read them, and the sense of the word is not a million miles from many of the others cropping up in this thread which go to the capacity to learn, distinct from the amount of knowledge acquired.

Personally, I think there's a set of outcomes here. To acquire knowledge usefully demands both retention and some ability to apply abstraction/synthesis to the knowledge acquired. Simply being a repositary of knowledge is not in itself usually useful, unless you want to win a competition for the most digits of pi, or ability to recite the Koran from memory, but latent within that ability are other skills which we often decry as "not intelligent" or "simply parroting facts" -the amount of facts you can recall aren't useful in the same way that synthesis over those facts is.