I don't know where the 45% number comes from, but it may be off a bit.

For example, this write up would indicate nearly 48% as the average: The Difference Between Boys & Girls - Part 1 - SPEED Theory. You may want to look at the chart of inseam vs. height on that page for some idea of normal. For a person 187 cm tall, the write up would, if correct, indicate that a 91 cm inseam is probably within one standard deviation of average, which is pretty close to average (I forget many of my statistics learnings, but if I'm right, 2/3 of people or things being measured are typically within plus or minus one standard deviation of average).