Why is this?

[Lilmikeishere]

For some reason, some member names are bolder then other names.

For example:



The names underlined in yellow seem to be the lighter ones, and the ones underlined in green are "bolder".

If someone can tell me possible ways as to why this is, I would appreciate it because it just doesn't look nice in my opinion.

Note:

All those underlined people are under the Registered Users membergroup, and their HTML markup is blanked out.

Could be a mod/product?

Any feedback appreciated.