Hemi,
Echostar one and two were only capable of using half of an Orbital Slots possible transponders. Both Satellites were only capable of using Only Even transponders or Only Odd transponders, they were designed to compliment each other, hence Both Satellites (1 and 2) were required to use both Polarities (Even and Odd). Since Echostar 1 can't use the other Polarization another Satellite is required to light up the rest of the transponders that Dish has licenses to use. The FCC can take back transponder licenses if a Company does not have hardware at an orbital slot to use those licensed transponders.
John