I think it's more common than you would suspect.

For me I toured nearly 15,000km up South America and Canada and I only crashed once and it was after 13,000km. It was crazy windy and I was crawling along at 8km/hr. I was fidgeting on the bike and staring straight up into the sky asking why I was doing this when I went into the soft shoulder and ever so slowly tipped over sideways. It was pretty much what you'd expect to happen if you stopped and forgot your feet were clipped into the pedals. It was pretty pathetic but thankfully I was in the middle of nowhere so no one witnessed it. I then proceeded to just lay on the road and stare into the sky for several more minutes. Stupid wind.