Since the details and reason for this policy seem worthy of capturing for posterity, I've drafted a brief handbook page, http://drupal.org/node/66113.
A small addendum. The LGPL permits the relicensing of any single copy of an LGPL library from LGPL to GPL (article 3 of the LGPL, http://www.gnu.org/licenses/lgpl.html). In three cases in the Javascript Tools package (jscalendar, wforms, columns) I have relicensed LGPL libraries to GPL and included them in CVS. Other modules using LGPL code, e.g., TinyMCE, presumably could choose to do the same. This practice is in full compliance with the GPL. I assume it's also in full compliance with Drupal CVS policies, as the software in CVS has only one license, the GPL. If there are any issues with this approach, please speak up! Otherwise, I'll add a note on this to the Handbook page.