On many UNIX systems, diff(1) doesn't show diffs of binary files. Therefore the CVS server's diff doesn't show diffs of binary files on some systems. As MacCVSClient does not calculate diffs itself but asks the server to do this (only the server has the necessary information for it), MacCVSClient doesn't show diffs of binary files.

Some versions of diff(1) do seem to show binary diffs. It can e.g. be noticed when running the CVS server on Mac OS X Jaguar or Panther. Generally those diffs of binary files don't make much sense, though.