To nappy or not to nappy - that is the question

I can't post pictures of toddlers without pointing out one part of their outfits that I still struggle to understand... Their nappies (or lack thereof). I still marvel every time I see a little one's bare butt exposed to the elements. Let alone the practicalities of guessing when the baby will decide to go for number one or number two and get the clothes out of the way in time. Or the hygiene factors that would keep every western mom losing sleep at night. But in winter, when kids are bundled up to the point that they can't keep their arms down - isn't it weird to have those pink butt cheeks exposed?