Maybe Dad simply thought it was funny. 
Maybe indeed. The part of the biography that I quoted from seems to have quite a humorous tone. Jamie and James, Jerrald and Jerry - success after name changes.
Speaking of which--"Dad" is one of Horner's more decent soundtracks, IMO. 
You're good at mentioning scores I've never heard of before - lol

Regarding Zimmer, some of what he has done is good, like
'Prince of Egypt' but he, and his team of composers, have blighted the movie business with a wave of empty gloss music in these past few years. I wish there were more chances for singular noteworthy composers rather than Zimmers team.
One composer I am keeping my eye on is Joel McNealy... a very clever composer, but has not been given a stand out movie gig yet.