Not sure what the magic is, though.
I did end up trying Parsec, since I saw some people recommending it, and that was terrible. Latency was fine (~10ms software <-> software) and video quality was alright, but audio quality was terrible despite being set to the highest option - which is especially bad, because there's no option to send uncompressed audio, and whatever "optimization work" they were doing to reduce bandwidth made their entire product unusable, despite the fact that there's no need to try saving 1mbps over a wired LAN.
the point still stands: most games are very playable via a steam link.