Personal Electronics on an Airliner

The title above has always comnfused me. Back in the days when most aircraft were flown with steam driven gauges and older technology in the instruments, I could understand the ability to cause signal disruption for navigation gear. The relatively low power of some NAVAIDs, the close proximity to possible antennas (or lead-in wires) of the personal electronic gear and so on. But nowadays, things are quite different.

Most airliners have much more sophisticated nav gear -- heck, even many of the ones still navigating by VOR and NDB have better receivers than in the past. Also, many electronics like radios and MP3 players draw less current from their power supplies, so they're less likely to give off any kind of RF which might provide for interference. One thing that surprised me last time I flew was the flight attendants' speeches regarding the use of electronics on board. They said radios were OK only at certain points during the flight, as were laptop computers. I would think that a laptop would be more of an issue than anything that is solely a receiver. I mean, the laptop has a hard drive and a CD-ROM or DVD-ROM (motors), a flourescent light behind the screen and a hot CPU with a cooling fan. All of this adds up to a high power draw and more likelihood of RF emissions than most receivers.

Maybe someone can explain this to me...? I'm sure I must be missing something.