It may be possible that they developed their internal compass due to their nomadic lifestyle and the use of absolute directions within language resulted from that (rather than vice versa). I have no idea if this is the case.
You can hear her account around 30 minute mark of this RadioLab episode: http://www.radiolab.org/2011/jan/25/birds-eye-view/
http://online.wsj.com/article/SB1000142405274870346730457538...
suggests that speakers of all these languages share the good spatial orientation abilities. Anyway it's true then that my argument doesn't hold. One should first verify if there is a subset of nomadic peoples that lack this language feature, and that they have poorer orientation abilities.