[Pseudoscience-is-malarkey (OP)]

...or is the ability mostly something one has to be born with?

Also, how important is for a musician to learn how to read music?

[alancalverd]

if you want someone else to play your music, it helps to write it down in a conventional format. The bigger the band, the more important it is to have a written score if you are going to play it live.

You can get away with playing by ear or memory in a rock or traditional jazz band, but it would be foolish to turn up to play an unfamiliar piece in an orchestra without looking at the dots, so sight reading more than doubles your potential income.

Strangely, sight reading seems to be a very British obsession and probably accounts for the success of the UK music industry. I've heard two impressive accounts of this. First, a Hollywood musical director who uses a lot of vox humana came to London to watch The Sixteen record a new piece. Apparently the guys sat down, looked at the sheets, then stood up and and sang it: two takes and the job was done. He said "We just can't do this at home."  And from Simon Rattle, who took over the Berlin Philharmonic Orchestra at one stage in his career: on his first rehearsal day he was shocked when the musicians complained that they hadn't been given their parts to study beforehand. 

I'm always impressed by composers and conductors of film music. An old chum used to write film scores without using even a keyboard. Translating  "38 seconds of puzzled anger" into something recorded in a single take is definitely a learned skill, but the fact that different composers have recognisable styles suggests that there is an undercurrent of inherent individual talent.