I don't know how Sun's support compares to the various commercial distros, but comparing an unsupported Linux install to a supported Solaris install isn't an apples-to-apples comparison.
What would be interesting however, would be a nice comparison of a supported Linux with a supported Solaris.
Then again, when you've paid for Linux support, do what is price difference between it and Solaris then? Whit is the price difference between a supported Solaris install and a supported Red-Hat install? Is Red-Hat significantly cheaper? Does it's less restrictive licensing bring about an advantage? Does it have features that compare with Solaris?
In addition to Red-Hat, Novell and supported Ubuntu are also worth talking about. Ubuntu may be free, but support licenses sure aren't.
You could also then compare supported Linux distros to unsupported Linux distros, but that's a whole other box of worms.
And those support contracts cost money, just like Sun/MS support contracts. And as soon as you start relying on software that isn't in their distro, you rapidly run into uncharted territory. The Linux meme of 'you can get support', is, I think, promoted mostly by people who haven't worked on critical IT systems, or have done so without understanding their responsibility.
That's not to say Sun's engineering is better than OSS (after all, we got their compiler to segfault as well as gcc, and my BSD/Apache shared hosting has had better uptime than my landline and TV for the last few years, and I'm sure many people want to set fire to the source code for NFS). Linux and other OSS provide the bulk of features that most people use. And you're probably better off with an unsupported apache server than some of the hideous commercial webservers that used to be around.
The bottom line is Sun charges a lot of money to mitigate somewhat nebulous risks that are hard to understand and communicate, and their OS has no killer features. They have also mastered the art of alienating potential enthusiasts. All of which put them on shaky ground. It is a shame, because platform diversity is one of the best defences of the internet as a whole.
(If you have access to dtrace, learn it. Understanding what it does and being able to use it will make you a better and probably richer developer).
Interestingly, I seem to have the entire opposite experience with unpaid support. If I asked nicely, I quickly got help about where to dig into the software and what to look for when fixing stuff. The programmers on the projects were quick to respond with requests for more information and suggested fixes, and often the problem was solved within a day or so. All I did was poke them on IRC.
No support contracts at all.
Linux: Seg-fault in the gcc toolchain. After casting about for several days, we couldn't even find someone willing to take our money to fix it. Digging into the code (ld), it's so cryptic it may as well be written in undocumented assembler. Responses from mailing lists and forums: "Go back to Windows" "Restructure your project to avoid that problem" "Why are you complaining, fix it yourself, it's open source" etc. We couldn't submit a test case, because it would have required making public a lot of code containing trade secrets.
Solaris: Seg-fault in the Solaris compiler toolchain. We called Sun, and were talking directly to dev tools engineers within minutes. They put the case on 24 hour support and had a patch for us to test a day later. We could submit a reproducible case because Sun accepted the code under NDA.
Not the kind of thing that shows up in feature bullet point comparisons, but when you have 30 developers held up on one side and the clients need the code to calculate their bid for an eleven-figure project (as in this case), it makes a difference.
In other words, Sun is at a disadvantage, since one of their main selling points requires an understanding of IT risks that most people, unfortunately, do not have. IT guys may think linux is 'cheaper' but they don't have their end-users' acute desire to minimise the already-remote chances of some random problem costing them millions in commission. Edit - it is also an unfortunate reality that being able to pin the problem on Sun (or Microsoft, etc) can save your career in a situation like this. There's no-one to blame if you are using open source and it goes wrong. The buck stops with you not just for your code, but for the code of any free tools you are using. I wish that wasn't how it worked, but there it is.
Plus, if you stay 'on piste' doing stuff that has been proven to work (you could hardly argue against Linux + apache for example), you have a relatively small chance of stepping on these engineering landmines.