I've always wondered the same thing - My theory is that at normal freeway speeds, the indicator points more or less at 12 o'clock, which is easier to see for a driver.
I think it's related to gear ratio and redline. My 89 Honda Accord LX-i needed around 3250 RPM to hit 70. The speedometer maxed at 130. If you extrapolate that's about right. I found out it was drag /horsepower limited to just over 100 but if it had the power the actual max before possible engine damage would be 130.
Of course this is based off one car so I could be totally wrong.