Every 40,000 miles is every 2nd year for the average American. Every 500,000 miles is once in a lifetime for the average American.
Using your own personal experience, it should be obvious that trivial fender benders are more common than once per lifetime but significantly less common than one every couple of years.
My household alone has had two fender benders in the past six weeks, one of which will not be reported (and, maybe not relevant, both the fault of other drivers). Zooming out in time they are less common but most are unreported. The big question would be whether the 40,000 number includes unreported incidents.
Using your own personal experience, it should be obvious that trivial fender benders are more common than once per lifetime but significantly less common than one every couple of years.