If you were to work at a firm for 50 years or stay married to the love of your life for 50 years, would you say that was a remarkable milestone?   Would one

They all convey water from point A to point B, they all have a level of structural capacity, and they all can be buried.  So, all pipes must be equal, right? 

As a corrugated metal pipe culvert or storm sewer ages, it is common for the invert to bear the brunt of the corrosion and abrasion damage.   Paving the invert