A little more time?
I think Amazon may be allowing a little more time for everyone to get the new software. I have three old Kindles -- two DX (B005 series) and one 2nd Gen (B002 series). I left them connected to a power source overnight with the wireless on, as directed, and not one of them downloaded anything. Yesterday I downloaded the updates from their website and tried to install them via USB. The DXs were fine; the update didn't seem to work for the 2nd Gen. Today, with the 2nd Gen's software still showing as Version 2.56, I connected it wirelessly to the Amazon store. Just to check, I rebooted the machine, checked the version (still 2.56), and again connected with no problem. I suspect they've realized that most people with old Kindles have no idea that they need to upgrade.