Nearly all manufacturers have this, it is there for a purpose and pressing the acceptance means you agree to comply wityh the rules regarding such devices. Sat Nav's are for guidance purposes only and the disclaimer is an aid to defferring responsibility from the manufacturers when Mrs jones decides to turn left on to a live railway track instead of the road junction just afterwards.
There was a case where one chapwas caught speeding in a 30mph zone when his external Sat Nav showed the limit to be 40Mph, his argument was that he was sticking religiously to the speed limit shown on the device...The speedlimit on the road had recently changed!
Just proves that there is no substitute for common sense and good eyesight.