The design team does a fantastic job of removing noise in the user interface of the Stack Exchange sites. Stack Exchange's main focus is on the content, the questions and answers, and that's reflected in the designs. Modifying the designs to make other elements stand out more could serve to clutter up the user interface and make it harder to focus on what's most important.
A user's usercard is not the most important aspect of a Stack Exchange post. Under normal circumstances, most people aren't going to care. However, it's there for the people who have spent enough time on the site to learn about this feature and become curious about a specific name to warrant checking out that user.
When you gain privileges on Stack Exchange, you get a notification in the global inbox with a link to the privileges you've gained. This gives you an opportunity to read about the privileges you've earned and even look through the ones you haven't earned yet. The people who care enough to read about this information will learn about it, while the people that don't care won't have to be bothered with something that doesn't interest him or her.
If I had to choose between making it more known to the outside world that this feature exists or keeping the focus on the content, the content wins every time.