I'm not seeing the downside.
If a user is posting good content, who cares what their user name is? If you're implying some sort of spammy-ness to the name they choose, I'm still not seeing the downside. They still have to post good content to get their name in lights. That's a net win to us!
The identity you choose is a personal thing. If someone wanted to be called (for example) "Ubuntu Fanboi", we wouldn't be having this conversation. So is a username like "AskUbuntu.com" really all that different? It's not indiscriminate advertising... it's a username; and it's not a part of the information content of this site. In short, there is no "spam" to a username.
Users have three major reasons to contribute to projects like Stack Exchange:
- Autonomy (work on something you enjoy);
- Mastery (be awesome at what you do);
- and Purpose
If that purpose happens to be a bit of self-promotion, we all like to show off a bit. So, we provide two places that allow you to establish your self-identity: Your username and 'about me' profile.
If we take away that little bit of self-identity, you're also removing one of the major purpose-driven motives for using this site… and that would be a disproportionate reaction to allay some momentary irk you assign to something so inconsequential.