We should sticky this thread since this will be the ultimate collection of famous last words.
I lived in PA for 11 years, and I had a Subaru the whole time. I started running two sets of tires, summer + winter after I spun out on NJ turnpike on my ALL SEASONS as I was coming home from Long Island. My all seasons worked just fine on that road for the first hour, that is until the moment I ended up in the ditch. Luckily I was going slow, no other car was around me, and the ditch was a pile of soft snow, so no damage was done, but it was still scary as hell.
The fact is that AWD does jack shit in making you stop. When your tires lose grip, how many wheels the power is sent to means absolutely nothing. Go to a Subaru forum, where people really know what they are talking about regarding AWD, and post your story about running summers in NJ winter. You will be laughed off.
And as for BMW knowing what they are doing, I suggest you send an email to BMW USA and ask for their opinion on whether you are operating your vehicle as the engineers intended. I think I know the answer.