> But if you take the point of view of a customer, it might not matter as much 'which' part is broken. To use a bad analogy, if my car is in the shop 10% of the time, it's not much comfort if each individual component is only broken 0.1% of the time.

Not to go too out of my way to defend GH's uptime because it's obviously pretty patchy, but I think this is a bad analogy. Most customers won't have a hard reliability on every user-facing gh feature. Or to put it another way there's only going to be a tiny fraction of users who actually experienced something like the 90% uptime reported by the site. Most people are in practice are probably experienceing something like 97-98%.