When you write a URL in a comment on Stack Overflow it automatically gets formatted in blue and made into a hyperlink. If the subdomain "www" is present it is not shown in the link text, but remain part of the URL in the href.
As I just did experience this might cause some confusion for the unlucky person who does not realise that there might be a difference between the link URL and the shown URL. Not a big issue, but should probably be an easy fix. I know that some people prefer to remove the www for readability and I agree that that makes sense for a general newspaper or an ordinary blog, but for a technical Q&A like Stack Overflow the extra precision is IMHO needed.