I've got the 19" Toyo A23 tires and I've had NO TROUBLE in the snow at all this year.
I've gone snowboarding in WV, VT, MD and PA this season and several times encountered snow. On two of the trips we had a storm which dropped several inches in WV and 12 in VT. Both times the stock tires did absolutely fine and I didn't even get close to getting stuck.
That said, I typically drive in 0-40 degree temps (F). So, I don't see the -20 temps when snow tires really help even more. I also haven't seen much ice, which snow tires help to stop on.
Bottom line, depending on temps you experience, the stock tires are fine.