The standard linear IC process is called "36 Volt", because breakdown starts about 40V and they take a 10% safety margin on the published Max, and prefer you work it at 30V (+/-15V).
IC processes are capable of higher voltages but there is a compromise with Beta. Hi-volt transistors in general have lower Beta, and in an IC you can't play some games possible in individual transistors.
I don't know for sure how 36V became the standard process. Some of it is history: much op-amp tradition comes from the tube op-amps with +/-100V outputs (on +/-300V rails!). 100V is a nice easy number to scale your calculations to. It was impossible in early transistor op-amps, so +/-10V outputs became the new tradition: again easy to scale. With losses, +/-15V rails are plenty. Take a 20% safety margin from rated-Max, which is set 10% below the tested-Max, and you cook the ICs to come out around 40V break-down.
40V was always what you got if you didn't fight for anything special. There were always a few high-voltage chips. 5534 is always specified +/-22V, apparently a slight push on the standard 40V process. Some newer chips exceed 40V. I'm suspecting that after 30 years of making analog ICs. and a declining analog IC market (at least for ~40V parts), foundries are now able to find an idle fab machine and tinker the doping and bake-time to make small runs of higher-voltage parts.
Discrete transistors are available in a wider range of voltages. Discrete production isn't as fussy as IC production so fabs are willing to deviate from Standard Process; less risk of making duds.
In audio, early board designers were fighting noise and later ones were exploring the far limits of S/N. The Burr Brown type op-amps were not at all great audio amps, so there was no strong tradition of +/-15V rails. And from transformer-coupled vacuum tube pro-audio there was a strong tradition of +24dBm and higher, which in 600 ohms is 16V or so. That implies +/-24V rails, and 50-60V transistors were readily available. So there is a whole world of +/-24V audio. The Jensen is perhaps the most famous (and most copied) but there were many others. BTW: most of these old-type modules will run very happy with +/-15V rails. The oldest ones needed a bias-change, sometimes not possible when the module was potted. Most made in the last 20-25 years will take what you give them (adding a bias regulator is cheaper than stocking 2 or 3 different-volt versions).
But the "headroom" difference between +/-15V and +/-24V systems is only 4dB. Usually if "X db" is not enough, 4dB more is not really going to do the job. And (ignoring interface traditions) the important fact is usually signal to noise ratio, not signal level. If you can find a +/-15V amp that is 4dB quieter than your +/-24V amp, you get the same S/N result. With less power and heat. And for whatever reason, +/-15V or +/-18V opens up all the ICs made on "Standard" 40V processing.
