So it's smart for Github to build tools that lower the bar for a) understanding git, and b) using git's more powerful features.
Useful metrics would be things like the percentage of users who use the pull request flow, use it with at least one comment per pull request, have pull requests that get revised, etc. etc.
I'd guess that part of the growth potential driving Github's valuation is the notion that git's power features add significant productivity/value and that github is uniquely positioned to let a significantly large number of developers and teams make optimal use of those features for development and collaboration.