Apple's failure and uncaring attitude
I've very little time indeed for Apple bashers !
Talk about making mountains out of mole hills !
How about considering the fact that its really a minor, very minor thing in the grand scheme of things and hence its utterly stupid of you to call this a "failure and uncaring attitude" on behalf of Apple. Fact of the matter is that that piece of code has probably been unchanged for a large number of years, because there's been very little need to fix bugs or otherwise fiddle with something that's working..... simple as that !
Quite frankly I think you're in a significant minority and think you would struggle to find any sort of substantial number of people who share your concerns over startup chime volume !
How about you consider that the sound chimes is at hardware firmware level, i.e.
BEFORE OS X loads and parses your preferences as related to volume levels ! That might also have something to do with it !
I just mute mine, works fine. The diagnostic purpose of the startup chime is minimal (and there are other, technically better, ways to diagnose startup if you care to bother read up on the Apple website instead of bashing them ....).
You may (at your own risk, I have not tried this and thus don't condone it, it is based on a bit of Googoo)... investigate the implications of what can supposedly be done with the "nvram SystemAudioVolume" command. Same disclaimer goes for the alternative of making use of LogoutHook/LoginHook and a quick shell script. As I said, you're on your own for both, so don't come back here asking me for detailed step-by-step instructions....
P.S. As an extra, did your searches come up with
this suggestion ?