Just doing a quick perusal of the top 5 projects listed at http://pypi-ranking.info/alltime
1 (boto) does not support 3.x
3 (distribute, zc.buildout and pip) only distribute non-version dependent files
leaving just 1 (lxml) with version dependent installers listed at all and it is only for the windows installers.
Drilling down into lxml, roughly 95% of its downloads are the version agnostic .tar.gz file. Also the version dependent installers do not include a 3.3 version but only 3.2 for python3. But even with only an installer for a old version of python3 available it still is >8% of version dependent downloads.
As a number of people have pointed out though, there's no new data since May 2013, no idea why (https://bitbucket.org/pypa/pypi/issue/33/package-stats-no-lo...), so the the '4%' number is probably out of date anyway.