I'd say the salesman was counting the commission on the Titanium Edition Focus, not worrying about how you'd get around in the Winter!
I'm not current on all the optional sizes for the '13's, but I THINK 16" is the smallest Std. size avail..
A set of those, with appropriate size Winter tires, should get you through MOST of the Winter driving you face. And you should be able to get chains to fit those to carry so you're "legal" where required. Going on through the pass when USE of chains is required would be at your discretion. (More than one Truck sits it out for a bit until the "chain law" lights go out as the road is cleared...)
Laws on the use of chains vary by state, year, and type of vehicle from what I've seen, & can change by the minute depending on current conditions in some cases.
In the few times I've been over the passes in the Winter myself, I've managed to avoid "throwing iron" - though I had to buy enough chains to be "legal" just in case!
Hope some 'Locals" from the states involved comment, at least you have some time to plan for next year at this point.