I've been riding down to -30C. Come to think of it, I can hardly recall seeing a backlava at downhill skiing slopes where temperatures below -20C might be common, with winds sometimes blowing so that you might fear that your head could fly off. Somehow backlavas are far more popular among riders on the flat at modest temperatures
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Well if you're wearing a huge winter hat, and a neck warmer and a scarf and have glasses or goggles, then yeah you don't need the balaclava/ski mask
Also downhill skiing not as representative of cycling as is cross country skiiing, because you go downhill for a few minutes at a time and can go inside whenever you feel cold.