I just want to add some information - years ago I held the exact same opinion as iNiq of various radio receivers until a couple of things happened.
First:
I got my amateur radio license and started building and tinkering with radio circuits. What I learned in this process is that most all digital receiver tuners work by running an oscillator at an offset of the intended frequency to be received and then tuning a circuit to the offset by means of a crystal. Well, oscillators are transmitters too, and since the whole setup is wired to an antenna some receivers can output a fairly strong carrier wave signal on the offset frequency from the one you're receiving.
An interesting (and unfortunate) example of this: Lots of digital PLL tuners use a +10 MHz offset frequency. So if you're tuned to 99.7 MHz with a digital FM tuner, the PLL circuit is sending out a "ghost" signal at 109.7 MHz. (You can often find the offset frequency with a handheld scanner, and then deduce what frequency the other receiver is tuned to.) What makes this example so unfortunate is that the aircraft navigation band is 108.0 MHz - 117.987 MHz. Simple FM walkmen can interefere pretty severely with VOR receivers in aircraft cockpits.
Sure, one stray signal in the back of a jet airliner might or might not cause noticable interference, but if you allow them and, say, 25 or 30 passengers turn these devices on then it can really wreak havock on the instruments.
Second:
I became a private pilot and eventually bought a Cessna 172. The darndest thing happened - sometimes my handheld Magellan 315 GPS didn't work worth a darn in the cockpit, no matter where I placed it. I fussed and fussed with this problem until one day during a flight I noticed that my second VOR Navigation receiver on my Narco MK-12D radio was acting weird too. I turned the Magellan off, and the VOR reaquired the signal from the ground station I was navigating towards. On the return flight, I turned off the Narco and the GPS signal came back. The two were interfering with each other - and only when the Narco was set to a particular VOR frequency. Another case of I.F./Offset frequency tuners causing malfunctions - and in this case the malfunction was actually between a handheld GPS receiver and a piece of aircraft navigation equipment. I was quite surprised, even though I knew it was possible.
So yes, it can happen. More easily than you think. In fact, now that I've isolated the exact frequencies it occurs with I've demonstrated it in my cockpit for a number of people as an eye-opener.
Pretty interesting stuff.
Cheers!
-pm