MJ
Ten years ago you would have been right - now (roughly)three modes L, P or M, the L is roughly the old military standard of ten years ago, typical accuracy with 6 sats is about +/- 300mm (dependent on RX)
P is an encrypted signal version of L and more resiliant to blocking
M is much more complicated and from 2013 will become even better due to the deployment of beamed signals to a specific area.
L is what civilian aircraft use.