Why Are Phono Cables Different?

I have now read from several different cable manufacturers that phono cables have different requirements than line level interconnects. What surprised me is that in the cases I know about the phono cable is always cheaper than the line level interconnect.

For example, Stealth's Indra retails at $5750 but their phono cable is "only" $2800. I would have thought that the phono cable because of the small signal to preserve would require more care and thus more cost.

Can anyone tell me what special characteristics a phono cable should have compared to a line level interconnect? (This would also probably tell us why the phono cable is cheaper.)

Thanks.
George