It matters because they are not forced by law to maximize profit. They can and do make decisions that are good for the future health of the company, such as making sure developers and customers are happy, and unlike other companies they put that 30% cut toward at least some things.
Regarding worker coöps, I wanted to respond to the other commenter and didn't know how to phrase it. I'm currently leaning towards describing myself as an anarcho-communist, though I'm not well-read at all. However I question a coöp could grow to a size comparable to Valve. From some things I've read about the company, their internal structure might not even be THAT far off from that, allowing employees to choose what to work on and such, even if it's far from ideal.
Finally, Valve has done much more than any other company considering they push gaming on Linux. Also their handheld is dope.