Author here. You're not wrong. There's nothing magical about DOIs or everyone would use them for everything and there would be no link rot. You can only update links if you know when and where things are moving, and you're still around to do it.

Scholarly publishing is an area where documents need to stick around for a long time, be able to be cited in a well-understood way, etc etc.

Crossref is an trade association of scholarly publishers, formed to solve exactly this problem. Part of the deal when a publisher joins Crossref is an obligation to keep the links up to date and a plan for what happens if the publisher suddenly vanishes into thin air.

Initiatives like CLOCKSS address the archiving question http://www.clockss.org/clockss/Home . The CLOCKSS homepage has a good overview.

And to the 'tracking stuff down' point, the DOI is resolvable (i.e. a link you can click) but it's also an ID that you can look up in a database. DOIs predate the web and may live longer than it. Having a single, 'official' ID (whatever it looks like) is better than searching by metadata.