I wouldn't say difficult. To set the high bit, the geometric mean of the two multiplicands has to be at least 3 billion. 32 bit numbers go up to 4.3 billion so that's quite common.

If I did the correct integral (the area inside the unit square above y=.5/x), then 15.34% of products should have the high bit set. That's much less than half but it's still happening constantly.