I noticed, that the sources zip is not available for download for JBDS 9.0.0.Beta2:
http://tools.jboss.org/downloads/devstudio/mars/9.0.0.Beta2.html#zips
There are only two files there:
Update site (including sources) bundle of JBoss Developer Studio (507MB)
Target Platform for JBoss Developer Studio (452MB)

Whereas the JBoss.org Products page contains the source zip:
http://www.jboss.org/products/devstudio/download/
Stand-alone Installer
Update Site Zip
JBoss Central Zip
Source Zip

Also, the JBoss Tools download page on tools.jboss.org does include the source zip:
http://tools.jboss.org/downloads/jbosstools/mars/4.3.0.Beta2.html#zips
Update site (including sources) bundle of all JBoss Core Tools
Sources zip of all JBoss Core Tools
Stand-alone BrowserSim
Release Notes

I understand that the sources are in the update site zip, too. But I wonder if there is any reason for this inconsistency. I can't think of any.