OK, here's the detailed version information:

Boot BLK B1350-00 2.30 Nuvi 40 Boot Block Software Pass
X-Loader B1350-00 2.30 Nuvi 40 X-Loader Software Pass
System B1350-00 2.30 Nuvi 40 System Software Pass
Basemap Erased
Suppmap1 Erased
PROM 1 Erased
PROM 2 Erased
Dlr DB Erased
Unknown Erased
Splash D3218-00 2.00 DB, Splsh Scrn,4.3in+3.5in,TTS,I Pass
Demo Erased
FTL ?????-?? 0.00 FTL Image
Audio D0397-00 2.00 English_Americal 07DF7F00
<lots more audio>

However, having slept on it, I think the Nuvi may be trying to tell me something. Namely that it may not a good idea to upgrade the firmware on a working device without a functioning USB port. This is because there would be no way to recover from a failed upgrade to either the boot loader OR the system firmware. On a device with a USB port you can always go into pre-boot mode and re-flash the boot loader. But without a USB port if anything goes wrong updating either the boot or system regions the device would be effectively bricked. Is this right?

Another interesting observation is that when I boot with the Nuvi connected to a charger (but the ID pin floating) I see the green progress bar growing for a few seconds and then it is replaced by the "waiting for computer" icon (GPS plugged into a computer). That icon stays there for 20 seconds or so and then the unit continues booting normally (without upgrading). But when the device is not plugged into power it just boots without showing the green progress bar at all.