This interpretation of the sound that those first three notes make has always bothered me. In all the years of my playing the game and hearing that song before I started seeing this pronunciation online, not once did it ever sound like "ɪ, ɪ, ɑ" (see here to understand those symbols), like the vowels in in, in, and on (in general American accent, to be clear), to me. If you listen to the vowel sounds that the piano makes as the strings are struck, there are a multiple different ways you could interpret them, none of which sound like "ɪ, ɪ, ɑ".

The first way you could interpret them is "æ, ä, ɔ", like the vowels in "cat, bra, and for".

You could also interpret them as "ɛ, ʌ, ɔ", like the vowels in "kept, rut, and for".

There are still more different ways you could interpret the sounds, showing that they are, in fact, subjective. However, that subjectivity is limited to how much you can stretch it. It is difficult to justify going all the way from "æ" or "ɛ" all the way up to "ɪ". Really, intentionally listen to the sounds the piano makes in the song, and see if you can really hear "ɪ", or in fact, a different vowel sound. Try to listen unswayed by the influence of how others have said it for so long.