After 530 miles, much of it highway, on my new 2013 RT, I think I've finally found why the machine exhibits instability at speed. As "KBFK" mentioned in another string, in this same forum, the sensitivity of the power steering, of some new 2013 models, seems to be more sensitive than older models. In further defining my experience, I am guessing that the electronic circut which governs variable assist (lowering steering sensitivity inputs as speed increases) is either defective or not programed correctly in my model, and perhaps other 2013 machines.
The effect is that the slightest movement of the handlebars causes the machine to get into a wobble when at highway speeds. At lower speeds, the steering is still very senstitive, but not as concerning as when at speed.
This may be a "one-off" issue with my machine, which I have an appointment next week to get checked out, or it may be a more widespread issue which has yet to fully mature as more riding experience with the 2013's unfold.
Bottom line: if you're getting serious about buying, or trading up to a 2013, I would recommend taking it out on the highway for a short test drive, and judge for yourself.
With that said, these are great machines. However, a re-program of the power steering may be necessary for the machine to reach it's ultimate purpose - that of a safe touring experience.