Rashi Wein

Soccer Dad notes Rashi's 900th yahrzeit as well. He also writes that

Rabbi [Berel] Wein estimated that 80% of Ashkenazi Jewry is descended from Rashi. Michael Gerver's calculations led him to believe that the percentage was somewhat higher.

Is that even a remotely plausible statement? It sounds really, really off to me. I honestly don't know what to make of it.