I've never liked Redmonk's choice of Github only. It's just one OSS host, albeit an important one. Why not use Ohloh's numbers (which they do reference), which cover a larger swath of the OSS community? By choosing to use GitHub only, projects that have been around a long time are not included--such as many of the active projects on SourceForge, Google Code, etc. Not to mention other currently popular hosts like BitBucket.