This probably isn't the issue for all of you, but if you are having other strange electrical gremlins on top of the not starting it is usually caused by a leaking windshield. Expeditions are well known for this issue. Water gets passed the seal, runs down inside the A-pillar and right onto the GEM and fuse box on the driver's side. I had the same issue with mine. I bought some high grade silicone, pulled back the windshield rubber and sealed it up better. As for the others, I'm not sure about the location of the safety switch on these vehicles, but I am having the same no start in park issue with a 99 F250 SuperDuty. I have to start it in neutral all the time. I have noticed that the shifter where it attaches at the column has wallowed out from heavy use. Not sure if there is anything inside the column there, or maybe at the transmission where the cable attaches keeping it from starting randomly. They put so many electrical things on vehicles these days they can be hard to find. If you can rule out the GEM, wet fuse box, or safety switches, I would say its a bad starter relay under the hood.
Not knocking the forums here by any means, but you might also search/post over at
http://www.expeditionforum.com/
The site is expedition exclusive with lots of info on all generations of expy's.