Normally when I am around town, all a thief will get is my bike, which could be a pretty cheap one. On tour there is thousands of dollars at stake, the future of the trip, and possibly a long way to the next bail out point. I take a reasonable quality U lock, but mainly I try not to leave my bike, ever. I don't sight see on tour, I am riding. Though obviously that is determined by the trip.

Cable locks do not deter much of anything. Cable is a pretty easy material to cut, I have rigging cutters for my yacht, and they virtually fit in the hand, and will shear 3/16" cable like a twist tie. BIgger cutters are required for bigger cables, but it is the same easy cutting action. There are areas where the idea of organized bike thieves is pretty far fetched, but unless you are that lucky the cable locks are mostly to stop the bike from falling over.

I think the idea that panniers mean you can't shackle a bike is silly. You probably can't get into into a bike stand, but you can lock the main tubes to anything solid you can lean a bike against and slip the shackle over.

I think the other deterant is that a lot of our coolest touring bikes are uncool versions of something our grandparents might have riden, and it takes an educated eye to see the value.