It doesn't require it but there are a fair few devices which are totally incapable of getting a GPS fix if turned on while already moving at some speed.
I have seen this in multiple PDAs, in a Thuraya 7100 satphone, and some other stuff.
I think the Ipad GPS, which is superb on the ground and even working pretty well indoors, is so good because it gets the fix over GSM first. In the aircraft it is much worse.