Not odd at all; the 4th (quad) band you refer to is the 850 MHz GSM band, which is used in North America. Since Nextel operates in North America and will not roam onto GSM networks in North America, there is no need for the 850 MHz band.

Same holds true for the new converged CDMA/GSM phones (like the Samsung A790), which uses CDMA for North America and GSM for international use. It has 900 and 1800 GSM bands, which are used outside of North America.