> IME (using a PPPOA ADSL service in the UK) turning off all NAT
 > functions on an ADSL/Modem Router allows the device to act as a
 > straight router which can then be directly connected to WAN side of
 > the WAN/OPT1 bridge in m0n0wall to allow devices to your network to
 > use real IP addresses (Certainly it works on my very low-tech Conexant
 > chipset based modem and a couple of others I've tried.)

That is exactly that one scenario where it would work. What you call a
"straight router" is probably the same as "bridging mode".

But not everybody is that lucky. For a start, we do not all have access to
ADSL :(