In this highly recommended interview by David Weinberger, open access advocate Peter Suber offers a pithy explanation of how open access means more than simply making scholarly communications freely available online:

Open access is not the end, it’s the means…to enhanced forms of research.

By making vast swaths of publications freely available online, we make it easier for us to design systems for text mining, meaning extraction, and automated classification and abstracting.

Definitely check out the full interview, which can be found in episode #2 (“Free Knowledge”) of the Library Lab podcast.