I think the BSDIFF40 part in the PTCH files is invalid.
For example the bsdiff part of ActionButton.lua from wow-update-12759.mpq says the resulting file would be 146789209322029069 Bytes long (thats 130 Petabyte)
As far as I understand the format the data in bsdiff files should be compressed with bzip2, but there's clear text in the .lua diffs.
I didn't find any file format beginning with 'PTCH', so maybe that's a Blizzard invention.