The ratios for the front and rear axle do need to be the same. Sometimes a slight mixing and matching of gears is required as certain axles will have a different final axle ratio(for instance, a Dana 44 will have 4.09 gears, a Dana 60 4.10, and a Ford 9" 4.11). This little difference in ratios is fine, but its not good to mismatch gear sets (for example 4.09 in the front and 4.27 in the rear). The transfer case(in our IH's) will always transfer equal power to both the front and rear axle.
Hopefully this all makes sense.