It seems to me that the first point made (on the performance of Squid's LRU caching) is really just that Squid is doing a bad job at it, and Varnish doesn't try

It seems to me that the first point made (on the performance of Squid's LRU caching) is really just that Squid is doing a bad job at it, and Varnish doesn't try at all (lets the VM system take care of it). In theory, managing memory at the object/application level should give you some advantages over doing it at the page/kernel level. I can imagine, for example, cases where Squid might perform better by moving entire objects to/from disk, rather than a page at a time in response to faults. In this case "1975 programming" really means trying to manage the memory hierarchy in the interest of performance, which is timeless. Indeed, the author later states that Varnish tries hard to "reuse memory which is likely to be in the caches", which sounds like the same idea applied to a different level.