(He didn't specify whether he was making a patch with VP2 or just a whole-file "patch" with autoplay.)
There were a couple improvements to the DeltaMAX patching engine between VP 2 and 3 that can result in smaller differences for some files, but nothing specifically targeted at powerpoint files.
If powerpoint files use compression, that can make them bad candidates for binary differencing, since the compression has the effect of hiding all the similarities between the files. You might be able to turn the compression off in powerpoint and see if that makes a difference.
--[[ Indigo Rose Software Developer ]]