On the contrary, many of us do realize that. The question must be put, however, is what are the odds of both of them failing on the same flight within minutes of each other? How often has that happened in your knowledge and experience?
What are the odds of flipping a coin and getting heads five times in a row?
Having flipped a coin four times in a row and got heads every time what are the odds of getting heads again if I flip it one more time?
I don't think probability works in the way you imply. ACARS fails quite regularly, once ACARS has failed what is the probability that the transponder fails? The same as it always has been for transponder failures. Unless there is a common mode failure in which case it is much higher.