Ahh yes, our infallible satellite tracking/transmission/receiving systems.
You do realise how often up/downlinks to/from satellites drop out because of things like storms, don't you. Let's just say they are not as reliable as you would love to think, especially as to get a signal from A-B can mean a few "jumps" from satellite to ground station and back before it reaches it's destination. A good storm in the vicinity of any of these up/downlink stations means no signal, as I'm sure we have all seen with TV signals.
Just because a GPS works in an aircraft when the weather is good does not mean it is possible for the system to be 100% reliable, and that is something anyone who has used such a thing or has any knowledge of sat systems knows.