Mixture,
No doubt you are right, but bear in mind that the lowliest soho router offers NAT plus SPI* plus port filtering, and often some degree of IP address filtering as well.
I'm not saying that a typical soho router is unbreakable, just that it is much stronger than NAT-only.
SD
* Stateful Packet Inspection, which addresses the TCP flag issue mentioned (for the less technically minded).