But you are ignoring a huge component of using github. If you only use github as a central, shared repo, sure you lost almost nothing. Their git infra seemed to be operational throughout this, but if you use the major features of github: issues, PRs, review, webhooks for CI, etc, you probably did lose out on developer time.
Me and my team pushed tons of code to origin today (JST btw), but we were almost at a stand still as far as merging to master and closing out branches. Github being down had a huge affect on the process -- review, merging and CI success. Merging was our big one since we have protected branches via github -- master; CI was second since we received no webhook events. So either we wait it out (~8 hours) or we throw out our process and do something different until they fix it. The later didnt seem like a reasonable course of action.
github != git
Its easy to say, "well they are down, that doesnt affect git", but the reality is that a lot of orgs dont just use git. They use github. That fact envelopes a lot of process, routine, infra, schedule, money, etc. Luckily, its only been one day. But developer time has definitely beem lost. You cant reasonably say otherwise if you use github.
edit: I will say I dont fully agree with the GP. Blaming the downtime on MySQL is silly and coming up with dollars lost is over the top. Things happen. That comment was a weird attack on a reasonably stable database. Github had a bad day; it happens.