Unfortunately, the test and release procedure would not be sped up very much by limiting the scope of the patch. If they were just changing one thing it should be much faster to test, but once you have a handful of changes you get into the full test procedure. Also, MS has limits on the size and number of patches than can be released, so it is better to try to fix all known issues and include any balancing changes and feature and updates, etc, or they could end up unable to add to the Xbox version. Presumably it is also easier to base the patch off the latest version of the code, rather than go back to the release version and make single-fix patches on that.
I don't know if this was changed in DKS, but in D2:ED the secret room in the Broken Valley mine only contained a couple chests with crappy loot.
