Well if they are still in fact being made then there must be some kind of demand for them. Perhaps to resellers for people that want exact replacement for repairs or perhaps educational training aids that have never been updated, perhaps Radio Shack buys them all as people seem to still buy them there. As you said there are better choices for general purpose op-amps.
Maybe Radio Shack is still selling the Forest Mims notebooks.
That's funny Nigel, although so true.
I never worked for anyone that used them, 1458s were popular dual op-amps in the 80's and I think LM358 was another. And man did the micro-controllers eliminate a lot of things.
There's a crap-load of stuff out there in the world that still requires it to keep the gear serviceable. Usually there's no time, money, or interest to adapt new or better parts.
I doubt it's much used anymore for new designs, except by some hobbyists, etc. I just checked National Semiconductor and the 741 in DIP and TO-99 are still in full production.
Right from the 70s it was the standard for decades in industrial equipment, especially analog DC motor drives,. Industrial drives are built to last a long time and there are still vast numbers in factories that need servicing. They havent been use in new designs for a while off course, its mostly digital these days.
(My guess is that people may have actually used it in SOIC for a short time, and since then Digikey, and perhaps other resellers, still have 'em in stock and likely can hardly sell them.)
I have some LM324, LM339, and NE555 (boxes of tubes) that I am sure are early 80. But you win on date. I think I have a 1976 NS ttl data book packed away .