Is note/key recognition by ear a must have ability?

[jancivil]

Absolute pitch without relative pitch means you're a jerk, not a musician. "They performed my symphony in D instead of C! It's ruined, ruined, ruined!" Avoid such people.

Why would anyone write in different keys, then?

Are all instruments we'll ever deploy working exactly as a piano is purported to with an equally divvied up octave into 12? Not even a piano does that trick. I mean you can't rely on a machine programmed to give exactly that result from end to end and come away with a piano anyone wants for musical purposes.

[PurpleCatfishBettie]

back in the day, the more i listened, and the more i played; the more i could hear what is going on. maybe it's the same for other people.

be that as it may, relative pitch is very helpful; identifying intervals and such. 'perfect pitch' is an ideal, but many never have it.

btw, 'perfect perfect pitch' would be where the listener could name the exact frequency number, and not a note name. (ex: 'oh, that's a 437hz, and that's a 2904hz', etc, etc.)

ymmv