Yes. CRAN R is licensed under the GNU General Public License (version 2). As permitted under that license, Revolution R is based on a modified version of CRAN R. The source code to that modified version (including a list of changes) is available for download when you download the binary version of Revolution R, as required by the GPL.
As an open-source company, Revolution Analytics respects the Free and Open Source Software philosophy and respects all free-software licenses. Revolution Analytics is also a direct supporter of the open-source R project: financially (as a benefactor of the R Foundation), organizationally (by sponsoring events and user group meetings), and technically (by contributing or modifications to CRAN R back to the community).
Hmm, that seems to be interpreting the GPL as closer to what the LGPL's intent is. I assume they're able to do this because their other tools (e.g. IDE) are careful not to actually link to R, but only call it via things like shared files and pipes?
http://www.revolutionanalytics.com/downloads/gpl-sources.php
And from their FAQ:
Yes. CRAN R is licensed under the GNU General Public License (version 2). As permitted under that license, Revolution R is based on a modified version of CRAN R. The source code to that modified version (including a list of changes) is available for download when you download the binary version of Revolution R, as required by the GPL. As an open-source company, Revolution Analytics respects the Free and Open Source Software philosophy and respects all free-software licenses. Revolution Analytics is also a direct supporter of the open-source R project: financially (as a benefactor of the R Foundation), organizationally (by sponsoring events and user group meetings), and technically (by contributing or modifications to CRAN R back to the community).