Well, to be fair, the changed pronounciations do make more sense. In east asian cultures there is no "ah" sound. And the western pronounciation of "avatar" makes sense when talking about the little picture on a forum, but not so much when talking about what an avatar is actually supposed to be - the incarnation of a spiritual being.
I'm not saying I'm a big fan of his or anything. But I do agree with the choice to use non-western pronounciations.
I'm not saying that the changed pronunciations in and of themselves didn't make sense*. I'm saying that they didn't make sense in light of, as you mention, M. Night's decision to change the races. What, so he cares about being authentic to the show's Asian roots, but not enough to not whitewash the characters? What sense does that make?! Argh. (Any frustration coming across in my comments is not directed at you, just to make that clear.)
* Although, I have heard from other Asian people that his changes didn't
actually make that much sense and were all over the place, linguistically speaking. It was like he was operating on some pan-Asian phonetic scheme, which is just silly because different Asian languages use different phonemes. In any case, the nations in TLA weren't all solely based on East Asian cultures. Heck, the Water Tribe were modeled off the Inuits. So not only did Shyamalan's decision to change the pronunciations seem hypocritical, but the pronunciation changes themselves were nonsensical, regardless of his claims that they had a linguist come in to supervise.