Actually, Teflon insulation is usually found as the insulator between the center conductor and the shield of RF cables. The higher the frequency, the more the current concentrates on the surface, so silver is preferred to any other coating, because it has the highest conductivity.
Of course, there is Teflon-insulated hookup wire, but that tends to be more expensive than most other insulations, so the extra cost of silver plating is relatively minor. And such wire is more often terminated by crimping than by soldering, and good crimp terminals work better when crimped onto something a bit harder than solder -- especially over time, so again, silver is better than solder tinned wire. The terminals made by AMP are usually silver-plated for the high end ones, or cadmium-plated for the rest.
Also, the Teflon insulation is at its best resisting elevated temperatures -- which would soften solder, thus reducing the quality of the crimped connection.
Enjoy, DoN.