That never takes into account remarriage rates. Lets say for example that 65% of people that divorce get married again. And lets say that about 30% of divorcees get married third time and that about 5% get married a total of 4 times. And the all end up divorced in the end. Now, if we assume that half of marriages do end in divorce we get a total rate that says 75% of all first marriages do NOT end in divorce.
Are you suggesting that 75% of first marriages do not end in divorce? I'm just saying that I can count the number of people I know who are still on their first marriage on one hand, whereas I'd need to take off my shoes and socks to count those who have been divorced. Results vary by generation, which may give mean and median divorce rates for America by generation that aren't at all similar.
At any rate, you're right in that the statisic is nonsense. There are no real hard numbers, since not all states report the number of divorces. It's all speculation, and irrelevant to any particular couple. They succeed or fail on their own merits, not on what society at large is up to.