This is technically true but the number of GitHub outages which have prevented you from doing that for more than a couple of minutes is pretty low. In comparisons like this, the more important question is not “is GitHub perfect?” but rather “what are you comparing it to?” — internal systems are notorious time-sinks and productivity levels from using GitHub normally are high enough that I think it'd be quite fair to conclude that you're still well ahead of where you'd be even if you have an extended coffee break once or twice a year.