Why do NOS Tubes sound better than new tubes?


Is manufacturing really that backwards in todays techno world? What is the real reason that todays tubes cannot equal the tubes of yesteryear?
tubed1
New tubes are a niche market, whereas years ago they were required by the most demanding applications.
Back then everything depended on the tube quality and stability whereas now there's an improvement of circuit engineering.
This was posted recently. You could see in the old videos how much they tried for quality. [http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1314237934&openusid&zzHifihvn&4&&]