I've never quite understood this for anyone but the biggest companies.
The vast majority of businesses aren't ever going to buy a red hat (or canonical) support contract. They're going to hire a Linux sysadmin to help them.
A sysadmin isn't going to be troubleshooting kernel panics that suddenly started happening on a production system, or why a new version of libfoo without a soname bump is causing service xyz to segfault.
Commercial support has it's advantages, and it is why I do plan on switching all of our CentOS VM's to RHEL in the coming year (especially since we've chosen to adopt OpenShift after a PoC with the upstream release). Honestly, why would we NOT, it's ~$2000/yr per physical machine to have knowledge that engineers are available should something go wrong in a mission-critical deployment.
> A sysadmin isn't going to be troubleshooting kernel panics
I would expect a sysadmin to do very basic troubleshooting, and if it's not a very quick fix, organise a new machine.
The sort of companies that will need to fix the issue on that box, rather than just replacing it, are the kind of companies that will buy a Red Hat support contract.
Let's take this example: Kernel update with security fix gets pushed out, said fix ended up causing issues with a network card or some other component and causes panics. Can a sysadmin revert to previous kernel revision? Sure. Should they have to do so, submit a bug and pray someone pays attention to it? I don't think that's a great idea.
Replacing hardware isn't always a solution, especially when it comes to specialized setups for databases, file storage, etc. Knowing your vendor has kernel engineers on staff that can tear through a kernel dump and get you a hotfix ASAP to test is important.
Startups may not care, smaller companies may not, but we're a medical billing company that has over 1,000 employees that need systems to be up - if they're down not only has work stopped but we're either paying employees for doing nothing or having to send them home unpaid (which makes THEM unhappy). Facebook having servers randomly kernel panicing affects their engineering team and causes small hiccups to their users (who don't pay them a dime), we have the productivity of our own employees and their livelihoods riding on the line.
The vast majority of businesses aren't ever going to buy a red hat (or canonical) support contract. They're going to hire a Linux sysadmin to help them.