Of course you didn't see postgres crumble. This still a toy example of a benchmark. Nobody starts (and even more pays for) a postgres instance to use exclusively as a cache. It is guaranteed that even in the simplest of deployments some other app (if not many of them) will be the main postgres tenant.

Add an app that actually uses postgres as a database, you will probably see its performance crumble, as the app will content the cache for resources.

Nobody asked for benchmarking as rigorous as you would have in a published paper. But toy examples are toy examples, be it in a publication or not.