That is a wild assumption with two key flaws

1. Windows in many workplaces has updates locked down too, except in circumstances where critical security or vulnerability patches are pushed through.

2. The same is true for many servers that run Linux.

As someone that works on tier1 services for arguably the biggest tech company right now, that's how it works in most of FAANG. Updates are gated, sure, but like with many things there's a vetting process where some things that look super important and safe just slip through.

In regards to your edit, I guess most cases are different from others, but if your entire business requires you to be able to use a machine 100% of the time then you should have the means to either use a different machine to continue transactions (ideally one with a known state that won't change, or has been tested in the last few months). If you need to log transactions and process 24-48 hours later do that on something that's locked down hard, with printed/hard backups if necessary.

Ultimately, risk is always something you factor in. If you don't care about 48 hours of downtime over several years, it's not a huge concern. I'd probably argue that many companies lost more money during these days than they would have spent in both money and people-hours training them on a contingency system to use in case of downtime.