Do I need a GPS in Alaska?

A few years back I read an article by some northern professor talking about the accuracy of GPS units in the north. The article was well above my pay grade, but he did mention, that in Alaska, almost all roads/highways are built in the bottom of valleys, hence no high passes like the lower 48, so for planned accuracy, your GPS unit has to be receiving the signals from 3 different satellites by direct line of site. In some of the valleys, at different times of day, you may not be getting 3 good signals for the expected 10 meter accuracy. Now this is not a problem when flying or boating as you are not in a valley. He also mentioned that reflected signals off the mountain slopes, beside your road can confuse your GPS unit, as they are arriving later than they should. However with all that verbiage, I think poor mapping in the GPS units is mainly to blame, for any location errors we run into.
Plus the accuracy of the units go up with the usage planned. Most vehicle GPS units are in the under $200 range, move into the marine series and the price jumps to closer to $1,000 and get into the aircraft Garmin Gps/etc/etc untis and the sky is the limit, easily into the $20,000 range per unit.