It's useful to be able to set the Expires header according to just the major (but not the minor) MIME type (ie Content-Type: major/minor), eg: ExpiresByType image/* "access plus 1 week" The attached patch adds this behaviour, and has been successfully tested on Solaris 8/SPARC with recent Sun patches.
Created attachment 1531 [details] Patch for this enhancement
There was change comitted into the 2.1 tree to solve your problem partially. It's proposed for backport. Marking it as fixed so far.