Indeed, TiG ...
"You might as well declare that voice recognition was non-obvious in the 1960s comp sci world simply because it hadn't been done."
As we all know, Star Trek had the concept of voice recognition computers in the mid-sixties ... and a lot of "Golden Age" SciFi did, too, back in the 1940s and '50s. The concept of "talking machines" goes back a LOT further, though ... See "Rossum's Universal Robots", for a start, and then look up the concept of "golem".
On the other hand, I question your "hardware limitations" comment ... My early 1980s C64 did voice recognition in the RealWorld[tm]. The unit in the car would unlock the doors, trunk (boot) & hood (bonnet), start and stop the car, operate the headlights and turn signals, turn on and off the radio and CB, and adjust the volume of both, operate the wipers, and sweep the windshield-washer squirter to irrigate the glass and/or passers-by, all on voice command.
The fact that I stopped playing with computers in cars (other than engine management) around thirty years ago, and why, is probably more of a story than the OA ...