We are working to normalize the CDN links to the different releases beginning with Ext JS 4.2.0. The links will be nested within ext, the license and version. For 4.2.0, the links for the GPL and Commercial versions are as follows:

http://cdn.sencha.com/ext/gpl/4.2.0/
http://cdn.sencha.com/ext/commercial/4.2.0/

Going forward, this is the format we will be using but will only be for the public releases. Support only releases will not be deployed to CDN but can be downloaded via the support portal at http://support.sencha.com/