At one level it really doesn't matter as the company is choosing who works for them, and the outcome of their action is the company's action. It's Valve's fuckup anyway we look at it.
At another level, qualified and well paid employees also take shitty actions. I'd argue they're often less prepared and less professional than contracted customer support.
Of course I do agree with you on accountability. Companies should not use volunteers for remotely relevant positions. If they do, and those volunteers screw up, it's on them.
But I'd contrast that with the reaction when people get rejections from the AppStore for instance. They're not blaming some proverbial intern for that, they'll rightfully blame Apple, either for inconsistent decisions depending on the reviewer, or lack of clear rules, etc.
Plus, most people using Steam uninstall games through Steam. So if Steam isn't cleaning up the registry that entry will stay there. I don't think the registry entry will do anything, but it can't hurt to remove it manually.