I've noticed that getting a link changed in some directories is almost impossible in some cases, and incredibly simple in others. One of the problems is the concept that the "link owner" is the only one who can do anything to report a change. In practice, anyone can tell if a link is dead, redirected, or changed significantly. But in some directories you can't even report this if you're not the original submitter. But what if the website has changed hands, or the original submitter was a SEO who no longer works for the webmaster and took the email and password necessary to change the link with them?
Damn good question. I was pondering this myself today. I wonder how many sites in my directories have been sold and reworked, how many are now MFA? There's too many sites to just go through them all.
I don't see an easy way for people to let you know if a site's changed in the blog directory in your sig. A good place to put this is on the details page, but I don't know whether there is a suitable mod available to do this. Alternatively, you could just put up a contact page, so people could tell you about dead links without having to report each one individually.