In a closed static system, water pressure is the same everywhere.
But in a dynamic system, you have to account for pressure losses. Basically, when ever water flows through something, it loses pressure (water meter, backflow preventer, valves, pipe). If everything was identical leading to the 5 heads (pipe sizes, pipe length, etc) then the pressure at the 5 rotor heads would be the same. Another way to think of it is that a rotor might need 30psi to properly work. So at least ONE aspect of the irrigation design has to allow a maximum of 30psi pressure loss from your water meter to the rotors.
Irrigation 101: www.irrigationtutorials.com