Why don't operating systems gzip their startup files?
dkersten: Linux DOES use compressed files - BUT: decompression takes time too, so I'm not sure exactly how valuable this is.
The real slowdown is waiting for hardware to intialise. The super fast linux booting that some people achieve is by clever elimination of services they don't need and by starting as many services as possible concurrently.
The real slowdown is probing which hardware is plugged in.