They are?! I would've had so much fun with that as a kid. Is this true of all Keens? 4 was my first and favorite.
http://www.shikadi.net/moddingwiki/RLEW_compression
Looking at a hexdump of the Keen1 file matches those specs. Keen 4 uses another, more complicated kind of compression, too: http://www.shikadi.net/moddingwiki/Carmack_compression
They might be thinking of earlier Id software games. Some of those weren't compressed, and you could at least edit them with a hex editor pretty easily.