development/test/prod environment & iOS releases ?

Here's a follow-up question:
How prevalent is it to create a separate LPAR to test a new version of
iOS with your Production programs and processes ?

I'm interested if there are places that separate out DEV / TEST / PROD
environments for program development, and even though they have the
ability to do multiple LPARs,
they just don't bother testing the new release of iOS because "IBM never
makes a mistake" or "it is just not worth the hassle"
or "the users will not take the time to test all the functions that
could break"
or "we have plans in place to roll back to the prior release" ?

Is it the case that the one-time setup of communications and file feeds
to a test LPAR for all users is too extensive?

Is that kind of thinking normal for small to medium shops, even though
they have the ability for LPARs?