Hmm, very interesting. I can actually click on a link from Amazon's software update page that says
Download Software Update 5.4.2.1 but as I've duplicated here, it offers up the old 5.4.2 firmware.
And if you try manually creating the link (all Kindle software updates come from the same folder but with a different firmware number) you get an error:
http://s3.amazonaws.com/G7G_Firmware...le_5.4.2.1.bin