Nokia are not very "big" over there. GSM is quite new to them - and Nokia did not make / make a lot of CDMA handsets (the "old" standard) in the USA. Motorola was the "American Dream" - so even GSM in the states got twisted a bit - so Nokia, Siemens and Ericsson could not supply equipment in time for 1. gen GSM rollout - but Motorola could.

So Nokia is not the market leader in the USA as they are in most other countries with GSM. (Nokia does not own the Japanese market either since they run another CDMA protocol)

So that is why Nokia does not get as many free cakes in USA as others might do. GSM networks does actually not cover ALL of USA yet. (See Sprint vs Verizon fx. :-) So potential client base for GSM handsets are no 98% of population like Europe - but maybe 40-50% depending on how you count.