I dunno. An op-amp is a high-impedance differential amplifier with (conceptually) infinite gain and monotonic behavior at the crossover. Hook it up in feedback to exploit those properties and walk away. Any other chip is going to work just fine as long as you aren't violating a voltage or output current spec or whatever.

It's true that it's possible to create a design that relies on a particular chip's behavior (like trying to drive an output directly and assuming it can do it vs. using, heh, a 2N2222 to drive the load). But those are pretty uniformly treated as "bad design". Op-amps "should be" jellybeans.