What benefits do customers actually get from the commercial distros except for support and ability to run certain "certified" applications (such as Oracle)? Are they really more stable/reliable? For example, RedHat vs Debian. 350$/year vs 0$. What can you say?
If you're a growing organization, sometimes the expensive option is actually the cheaper option. Having access to high-quality support and training courses is an advantage in many situations.
Another factor is how do you manage applications? If you're going to roll out an app, and just want to leave it alone and patch security vulnerabilities for 5 years, that's more viable with something like Suse or Red Hat.
We use Ubuntu and Debian servers in my company. My system admin screamed for ages to install RedHat but the CEO wanted to keep the IT landscape the same.
In my company we have 6-7 people with A LOT of Debian/Ubuntu experience and we can basically get anything done very quickly.
When I came into the company I paid for 2 Ubuntu servers to have support for a year and I haven't even used it once.
So basically, what I am saying is, depending on the experience of the people of your organisation. If its not that great, then get support. If it is, then its not really needed.
The question to ask yourself is: how many other people need what I need? If you're doing what everyone else is doing, it makes sense to outsource the bulk of the work to a specialized outfit who can hire kernel engineers, monitor bugs and security patches, etc. RHN can make managing servers much easier. I should note that Canonical offers a similar service though I haven't checked their prices.
However, there comes a point when your organization wanders past the run of the mill. At that point you need experts who can do all that with an eye to the breadth of possibilities. For example, the Sanger Institute originally ran their Human Genomics servers on a proprietary UNIX that could handle 64bit filesystems and so on. They later moved to Debian and build a custom Linux kernel that met their needs in the late 90s when their hardware support was discontinued and other unfortunate events. Two of their employees were Debian Developers capable of making all that happen.
It's tempting to price a community distro like Debian at zero and hire novices to handle things, but I believe it's more expensive in the long run when your novices failed to plan for things Redhat and Debian Developers are aware of. If you run Debian and don't give your admins the leeway to pursue Debian contribution, you're losing a lot of valuable free peer review.
In short, the price of Debian isn't 0, it's the price of hiring a DD or two.
The lines are blurred with this question though, as you've got to be able to compare distributions such as Centos and RHEL, both of which are built from almost identical packages, just one has commercial support.
As I've seen it, the difference between Centos and RHEL are very small, especially if you don't require the support contract.
You're paying for support, which can be extremely valuable. I've worked tech support for a major hardware vendor and we routinely got RedHat, SuSE, and Oracle to release patches/fixes/updates when we found a bug that crippled a customer's solution. Within hours or days, depending on the severity.
With a free distro, you're at the mercy of the community (or can patch bugs yourself).
As a consultant, now I recommend CentOS, Debian, or some other free distro for simple, tried-and-true solutions that I already know work out-of-the-box, such as a simple firewall, squid proxy, http server, etc. I recommend distros with support contracts for anything complicated where encountering bugs is a high probability, such as Oracle clusters, HPCC solutions, and virtual machine servers/clusters.
RHEL comes with management benefits that CentOS doesn't - the Redhat Network management tools that let you handle channel subscriptions, package installations etc to your servers are the best single example I can think of. If you've got a lot of RHEL machines, then a system like RHN or a Redhat Satellite Server can really improve things.
Canonical are offering a similar kind of system, called Landscape, which is provided to all of Canonical's Ubuntu paid support customers.
These tools are in addition to having helpdesk/support services, so you're not just paying for those items.
Thanks to the commenter: I didn't know about spacewalk. Looks good.
Day-to-day, I think it makes very little difference. In fact your organisation might benefit more from the free alternatives, with their typically more up-to-date packages and vibrant community support. It depends on what you need.
As a small software company, we chiefly use Fedora and OpenSuSE but we specifically choose more than one distribution to help prevent us becoming locked to one variant - as our customers use a wide range of distributions and what would like to see distribution specific issues before them! That also gives us a broader base of expertise for supporting our software on unexpected platforms (as we'll provide support for any platform the customer pays us to!).
The commercial support can come in handy if you are doing some very deep development and need to know how the kernel does different things.
Otherwise, it really depends on your applications and how often you need updates and your business depends on updates (i.e. security audits)
CentOS stays pretty well updated, but there is no guarantee. If you need a guarantee then use Redhat or SLES.
If many of your security issues/updates deal with open source (like ours do) then we just use the Base OS and then compile openssl, apache, mysql, php, etc. from source. Because support for those open source projects are much better. In fact you will be able to update faster getting from source than waiting for vendors to update their versions of those apps.
Long story short: if your business depends on contingency plans of Kernel updates and support, go commercial. Otherwise, go free.