Just to clear up a few things. The performance tires are made of a compound that is extra soft and sticky in normal temperatures, but they get hard in the cold and lose their performance. Winter tires are designed to be softer in cold weather. The tread patterns are also different to accommodate ice and snow vs. just rain. So, without a doubt summer/performance tires are not nearly as good in cold weather or snow/ice. The other reason it isn't recommended, and I haven't seen anyone bring this up is that below the rated temperature the tires can develop cracks if you drive on them. Look up the specs and it will say that if the tires go below that temp, they need to be slowly brought back up to a normal temperature and sit for a certain amount of time before you can drive on them.
That being said I believe the 4Ss have that limit around 20 degrees, which is pretty cold for where I live. I have driven summer performance tires (Goodyear Eagle F1, Pilot Super Sport, and most recently the Pilot Sport 4S) year round in winter, including snow. They slip and slide but its nothing you can't manage if you drive cautiously and understand that your traction is limited.
Not sure where you're located but if you get harsh winters and regularly have temps below 20F, I would recommend getting some all season tires or investing in a cheap set of winter wheels/tires.