I think some people are missing this point:

"Recommended Plugins tab that takes into account the plugins you have installed and suggests plugins based on which ones are commonly used together."

This is the key point. The results you see on that page are based on what plugins you have installed and what plugins other sites are using. It's totally automated data, basically.

That said, you're highly likely to see some high profile and commonly used plugins which you don't already have. For example, Contact Form 7 probably is in your results if you don't have it installed, because a lot of other sites do have it installed and are also using a lot of the same plugins you are.

That's how the Recommended tab works, it takes all the plugins each site uses (based on the update checks), and builds statistical similarities between them. So based on the plugins you have installed, it tells you other plugins that fit similar profiles to that set.