That's not accurate. Every GPS receiver in existence uses filtering. The question is, how sharp does that filter have to be? The GPS frequencies were chosen to

That's not accurate. Every GPS receiver in existence uses filtering. The question is, how sharp does that filter have to be? The GPS frequencies were chosen to be away from frequencies used by transmitters that might be near GPS receivers. Lightsquared proposed repurposing satellite downlink frequencies (which they bought at a discount because this restriction limited their use) for the purposes of terrestrial networking, breaking that assumption. In order to maintain similar functionality, GPS receivers would require significantly sharper filters, increasing bulk, cost, and complexity.