I'd be much more impressed if they don't "scale" their employees at all. Github can not possibly need 40 employees at this point. Nothing ensures eventual mediocrity like hiring masses of people.
GitHub actually has a lot of systems with a lot of features, and a lot of competition. Not everyone uses all of their major systems other than repos (teams, issues, wikis, sites, GitHub:FI) but many do. If GitHub only worked on their core product, many valuable customers would leave for competitors.
