[jjoonathan]

Rain and fog are the traditional enemies, difficult to defeat with redundancy. I suspect the answer is that downtime does happen but customers value the price/performance more than they dislike the downtime. The steepness of the tradeoff also probably depends on local climate, but that's a blessing as well as a curse: initial deployments can preferentially happen in advantageous locations.

[mildlyclassic]

Could not have said it better myself. One more thing, keeping the units within 2-3km pretty much negate the rain/fog issues.