taking away support, what does any commercial linux/unix have that a free one does not? are the commercial ones faster in some way? or if you know what you are doing with lets say Slackware or FreeBsd, could it be used for a supercomputer?

There is no real difference other than support.

Some distributions that have free and pay versions will strip features out of the free version to try and get people to by the pay version, but there is no technical reason for that, it is an artificial limitation.

There is, by nature of the way open source works, nothing you can do on one distributions that you can't do on another. Things might be a little different between each one, but the whole concept of the GPL ensures that no distribution can create a proprietary feature that the other's cant copy if they chose.

There are some UNIX flavors such as Solaris that have fancy features (such as predictive healing, etc), but in almost every case there is a free program that will do the same thing.

When you pay for such software, when your boss comes breathing down your neck asking why X is not working, you can say that you will call up the company and ask them, rather then fixing it yourself (and taking the blame if your fix does not work).

Incidentally, that is one of the primary reasons that small businesses are reluctant to switch over to Linux or OSS in general. They want somebody to clearly point the finger at when something goes wrong.

Same reason those business would rather by overpriced Dells than have somebody build their computers for them (or at the very least get them from one of the smaller computer manufacturers).

They want to know there is a huge company out there that will fix any problems they have, regardless of how well they actually will do that.

They can also provide you with some form of protection against certain technologies through their licensing of such. For example Mp3 Codecs do not come standard with a lot of distros (whilst perhaps not useful for your scope, it illustrates the point and could be used for anything else).

Some commerical distros are also singulary supported by certain apps. Such as Orcale only supported it's use on Red Hat until they released their own distro.

I'd hate to have to explain why X won't work on Y when Y wasn't on their supported list to begin with. (which ties in to accountability for problems, as has already been mentioned).

I've never used a commercial disto, i have never need to.

When you have the choice to compile your own programs and kernel, how much 'better' can any other distro really be, in a technical sense.

Commercial distros may include proprietary (third party) software which is not included in the free version.

In re support, with commercials distros you get installation support. You can buy more comprehensive support contracts.

you often get a printed manual aswell.

our fully comercial solaris sysyems at my work (very old solaris 2.6)
came with several manuals, (taking up a whole bookcase,)