It's not about update frequency. It's about vote-totals:
While 28 people have voted here this month, no one's voted more than 10 times. The votingest voter has cast only 8 votes. So, no one meets the 10-vote threshold for display on the page.
This shading indicates that you can mouse over the image to get a summary of a higher reputation user's profile.
The feature is known as a user card mouseover popup and appears to come in at a reputation of 1,000, but only if the users profile is complete and long enough - see How does the User Card popup work?.
Many, but far from all, of our highest ...
I don't usually bother deleting comments. When I do, it's usually for one of these reasons:
The comment includes inaccurate or misleading information. In this case, I delete it to prevent anyone from being confused or mislead.
The tone of the comment was overly harsh, judgmental, or mean. (I mean, who hasn't occasionally wanted to shout "Read the d--m ...
Yes, obsolete comments are disruptive and can waste people's time if we unnecessarily read them thinking there is something important there. I believe it is also hard (in the sense it is time consuming) for moderators handling flags raised on obsolete comments (but not sure, not a mod).
On the other hand, it is cumbersome and boring coming back and ...