[syntheticnature]

One thing hinted at by the other comment thread, but not brought up: in the embedded world, read-write filesystems as you know them are less common, and usually a failsafe mode is desirable. OpenWRT, for instance, uses a JFFS overlay on top of a squashfs (at least in a recent-ish build for a router I have). So you change out the squashfs (and try to figure out what to do with the overlay filesystem), rather than replacing individual files.