At least in my world, our banks and trading partners like to make sure we have outside support, in case one (or all) of us gets hit by a bus. That's only being responsible. Our best-supported (and most important) systems are RHEL systems. Then again, we are probably what you would consider a medium-to-large US company.
Unless your scope is kept very shallow and/or very focused, you will never be doing anything more than tweaking applications or simple debugging. The codebase for most apps is too large and if it's not your primary job / hobby then you won't have time to learn it, let alone keep up with its development.
It's wise for each company to know where they stand when making any IT expenditures, whether the goal is to have a large Help Desk for instance or outsource everything beyond a certain scope. I don't run cabling anymore, and although I could if needed, we pay contractors for that stuff. Just like I implement systems using MySQL, but I don't tweak its source or try to perform bugfixes myself (beyond Googling for answers to questions) because I have other things to do. I support other databases and systems, and I have other apps to code. My time is most valuable to my employer for these tasks, and I'm a lot more expensive than spending a few thousand a year per server for support.
Need an example? OK. We successfully implemented a fiber card in 2 of our blades (RHEL 5.4 with kernels from 5.1) and this week brought up a third blade (same model, same base OS) only this time using RHEL 5.4 with KVM for virtualization. The kernel is 5.4 and the HP drivers won't install. The issue appears that one of the RPM's (lpfc IIRC) won't install because 5.3 and higher is not supported. The support grid at HP says that 5.4 is supported. Now I need to implement the entire tested solution by the end of next week.
Do I want to play around with this? No. I have one of our network admins contact HP and work it out, and when they're finished, give me a written set of instructions which I will add to my documentation. That's how larger businesses handle this stuff.