Did you look at those two files as plain text as well as via ghostscript or similar? I'm not familiar enough with postscript to understand how the 5 characters changed in the binary bit at the top can cause two otherwise identical documents to appear so different when formatted?

I looked -- actually there are 7 bytes that differ:

byte    value in  value in  xor
offset  "letter"  "order"   diff
--------------------------------
0x53      97        17      80
0x6d      a3        23      80
0x6e      78        79      01
0x7b      5a        da      80
0x93      c8        48      80
0xad      d8        58      80
0xbb      6f        ef      80
[download]

Obviously there's some clue here about how md5 actually works. As for how this example was implemented, I can easily imagine putting both texts into the single .ps file, and using some binary differences at the top to toggle between ignoring (i.e. not displaying) one text or the other.

Kind of reenforces my distaste for non-plain text communications mediums.

Amen to that.