Can you tell me where http://www.youtube.com/watch?v=2pMM4iwC-ag goes to?
Now, if I instead said it's YouTube — Queen - Somebody To Love, wouldn't that be more helpful to decide whether you want to go to the actual content provided by that link? You can still check the link in the bottom left corner; but don't worry if you have an up-to-date system, browser and a scanner...
As for dead links, that's why we ask users to include a summary in their post for when the link dies. Similarly, if the first link died you wouldn't have known that I meant to link a Queen song.
Of course, there will always be the uncertainty if this link is a Rick Roll or not, unless you memorize IDs or have a tool to request video titles by their link. But in general, links are not always right but we can do our effort to make them more readable to the reader in the sense of the content they will provide.
I think that you can also assume that links that point to spyware or loudly playing pornographic content will get edited out in a matter of time, or perhaps the post would even be flagged and deleted by a mod...