Sniffing and Spoofing Outside Your Router

Seeing some tech available and my limited networking knowledge, I had some questions.
The tech: http://www.haxorware.com/
Is it possible for someone in a cable modem style network to use this tech to sniff and spoof?

Does provider equipment prevent this attack scenario?

In my neighborhood everyone feeds off of the same cable line.
Are the packets "multicast" over the cable line, but ignored by the NAT on the consumer modems or routers if the packet doesn't belong to them?

My internal network is 192.168.x.x, the network address used outside my consumer modem is 10.0.x.x.

R=consumer cable modem, I=coax, LGD=Local ISP Gateway Device, H=Haxorware modem

H-----I
R-H---I
R1----I
R2----I
R-----I
R-----I======LGD
R-----I
R-----I
R-----I
R-----I
R-----I

H can spoof or sniff any R.
R1's Nat ignores neighbor R2's data but data is multicast in the physical neighborhood until ISP device.
Is this view incorrect?