Right. So the US defying the UN matters in terms of real-world effect, but the UN defying the US doesn't.

In the analogy here, wouldn't the W3C be the UN defiantly making toothless proclamations that Chrome (the US) can simply ignore? That would be my understanding of it, since "mattering about as much" implies not mattering at all.

The ICC is independent of the UN. Also its treaty based so you have to consent to its juridsiction at least once (or have the UN security council give it juridsiction) so of course there are no consequences for countries that haven't signed up. Anyways this is a really bad example (you are probably trying to reference invade hauge act, but even still that doesn't fit.

US does ignore UN in other ways, but the ICC isnt an example of that.

The UN and the ICC are two different organizations (maybe you're thinking of the ICJ?), and the US isn't party to the Rome Statute either. That said, yes this law is dumb.