Anyone who has been running a website for a few years (and paying attention) will be familiar with the reality of link rot. Sites get redesigned or removed from the web and, in so doing, links you have made to them in the past cease to be functional or lead to the right content.
Unfortunately, there isn’t a huge amount that can be done about this. For the people doing the linking, there is only so much effort that can be devoted to making sure old links are still current. It is feasible for a few critical links (blogroll items, links in key posts), but not in the case of hundreds or even thousands of old entries. If the content had been moved, there is at least the theoretical possibility of combatting link rot through updating. If the content is simply gone, there is really very little that can be done.
Those being linked can probably do the most in response. When they move from one type of site organization (or one site location) to another, they can provide tools to help those brought in through old links. The gold standard is to automatically redirect people to the correct pages in new locations. At the very least, sites should provide a mechanism for lost visitors to search for the content they wanted.