I don't think Scribd has much of a chance against the Open Library:
Not a chance ;)
http://www.techcrunch.com/2007/08/13/alexa-says-youtube-is-n...
The chart you mention just shows that Open Library users have enough common sense not to install that crappy spyware Alexa toolbar.
Apparently they also have enough common sense to prevent their ISP's from logging their traffic and sending it to compete.com ;)