The combination is most likely, but depending on the website, there are different metrics. For many sites, it's all about conversion. If it didn't sell, it didn't produce. But some websites are a slow burner. Sometimes people need several touches before an interaction happens, so in those cases, we're tracking the analytics of things.
The metrics here on HD are most likely in the length of time, bounce rate, and interaction (number of posts/replies). And that's all good and well but it doesn't "directly" pay the bills. When tracking the advertising page, sponsorships, etc, those use completely different metrics to track.
The local locksmith only cares about how many times the phone rang. The apartment rental company wants to see how many people viewed pictures and went to the contact page. The auction company wants to see how many times things were shared potentially increasing the price at an auction.
Lots of metrics, but every site is different. And even then, my definition of a successful site, and a client's definition, can often be two different things too.
