I guess the article is written from the perspective of AVID: once electronic headphones became cheap enough, they didn't sell any more pneumatic systems for air

I guess the article is written from the perspective of AVID: once electronic headphones became cheap enough, they didn't sell any more pneumatic systems for airlines - but the last planes equipped with pneumatic systems in the late 70s/early 80s still flew (unrefurbished) until the 90s.