be -ingに関する質問です
"I'm going to New York next year."という文章には、will be -ingほどの確約がなく、いつNYに渡るのかこの文章からはわからないそうです。
be -ingは近い確実な未来を表し、すでに段取りを進めていることを示唆すると思うんですが、なぜこのような解釈になるのでしょうか。

以下、ネイティブの解説です。
the simple future is used when the future event is definitely going to happen, "I will be travelling to New York next Wednesday." - this will definitely happen.
Whereas the present tense together with a time reference doesn't have the same commitment, "I'm going to New York next year." - sometime, probably, but not totally sure when.

また、この質問に関連してこのような解説も発見しました。が、これもどうしてそうなるのかいまいち飲み込めません。
Q: "Will you dry the dishes?"
Answer 1: "I will" (an affirmation, a promise, a positive statement)
Answer 2: "I am GOING TO!" (a whine, a complaint, the thing a teenager says to her parent)
The difference is a little subtle -- in the first case, you can replace "I will" with "I promise to, dear Mother"
while in the second you could replace it with "I am going to get to that, sometime" or "I plan or intend to at some future point, but not now."

よろしくお願いします。