I didn't work for HP and have never seen a flash Jornada 720. I think they were just manufactured with Intel StrataFlash on the main board instead of mask ROM.
The early iPAQ models had Windows CE in flash, so you could easily overwrite it. Back then NetBSD didn't have a flash filesystem so NetBSD/hpcarm just booted from WinCE and ran in RAM.
The handhelds.org distribution was a DEC/Compaq/HP project that initially targeted their Itsy [1] device, then added support for their commercial products as they were released. Later they allowed external contributions too. They build an iPAQ sleeve that contained accelerometers to be able to carry on the UI development from the Itsy, you scrolled the screen by tilting the device. Their Linux kernel did have a fair bit of power management built in.