I agree that the post would be more compelling if I wrote a benchmark to demonstrate how much faster an in-memory cache is than an off-process or off-machine cache.
From first principles, though, I believe it should be obvious (yes?) that the ~300 nanoseconds it takes to grab a read lock and read from main memory is going to beat the ~1000000 nanoseconds it takes to get a response back from a remote cache over the network. Inasmuch as an application blocks on such cache reads, these sorts of things add up to troublesome latency numbers (and Rails – or at least dallistore – does indeed block on reads like these).
JRuby was off the table for the place I used rails due to reliance on some C extensions.
And I'm sorry if the argument seemed arrogant: I was being tongue-in-cheek about the "unrelenting negativity" part. My point about objectivity was that I tried not to rely on my opinions as much as demonstrable statements. That said, I didn't take the time to actually demonstrate most of those, and for that, shame on me.