I will try to be brief but this is a complex question:
Imprezas make their power down low and in the midrange (torque peak is 4k).
Hondas, on the other hand, make all their power up top...you have to rev them to the moon to get good power.
Larger displacement motors don't have to rev as high to get good power and often will have a mechanical failure if they are revved too high. With the Honda VTEC, the car drives normal until about 5500 RPM...then all hell breaks loose and you can make decent power all the way to 8000 RPM. The Impreza starts dropping off around 5700 RPM so it is useless to keep revving at that point. You want to shift so that you will be as near the torque peak as possible. In the Impreza, shifting at 5500 RPM will put you at about 4000 in the next gear...this is the peak and where the car is developing the most power. So that is why some cars rev higher than others...it is all about where the power is...the 6200 Rev limiter on the Impreza is conservative and the engine can take a lot more...but why? The higher you rev after 5600 RPM, the less power you make.