The vast majority of the traffic that hits Sourceforge is there to download software, not contribute to the projects. When we spoke to them a few years ago, they said their main competitor was Downloads.com not us (GitHub).
Don't get too caught up using graphs to assume relevancy, Myspace still gets a lot of traffic.
Quantcast: http://www.quantcast.com/profile/trafficGraph?wunit=wd%3Anet...
Trends: http://trends.google.com/websites?q=sourceforge.net,+github....
Alexa: http://traffic.alexa.com/graph?&w=400&h=220&o=f&...;
By what measure are you talking about? Ah of course. The "It's shiny new so hot right now within my small circle of friends!" metric.