It is less well known that this story is bullshit. The people who talk about scientists proving it to be true neglect to mention that the results are hundreds of years old, or that they involved very specific circumstances. By and large, frogs don't sit still for you.
However, nobody really cares about boiling frogs (at least not in this manner). The point of the story is analogy. People more easily ignore changes when they happen in small increments. The mind has time to adapt to new circumstances and forgets that things were ever different when the next minor change occurs.
So here is the question, and it is one I don't yet have an answer for: if people have a metaphor which is commonly known and regularly used to explain a standard human phenomenon, does it matter if the metaphor is based on a complete lie?