Yeah, unless you tinker with them a bit, they can be rather sloppy on the band, but they aren't bad. My first xtal radio kit was a radio shack special, and with the way I worked it (I was 9 at the time) I could get KGO out of San Francisco at night from Seattle (granted they pump out the power, but it is possible to pick up the long wave with them if you finesse it).
Really, the items sold as xtal radios today aren't, they use the low voltage diode junction as the detector, like you say, which is fine. In fact, it makes the kit that much less expensive and more rugged I think.
You do get to the crux of my vision, which is that if you know a little about the technology, it is easy to come up with a "xtal" radio circuit by scrounging on powered radios that no longer have a power source. Wasn't that a Macgyver episdoe? <img src="/images/graemlins/tongue.gif" alt="" />
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The ultimate result of shielding men from the effects of folly is to fill the world with fools.
-- Herbert Spencer, English Philosopher (1820-1903)