Yeah, I've gotten somewhat annoyed by the name of 'NAT traversal' for these methods. It seems to make some people think that cutting out NAT will lead to a beautiful world of universal P2P connections. But really, these methods are needed for traversing between any two networks behind stateful firewalls, which will pose a barrier to P2P indefinitely.

Also, wouldn't it be easier for stateful firewalls to block simultaneous TCP open (intentionally or not)? With UDP, the sender's firewall must create a connection as soon as it sends off the first packet, even if that packet bounces off the other firewall: the timing doesn't have to be particularly tight. But with TCP, the firewall might plausibly wait until the handshake is complete before allowing incoming packets, and it might only allow the 3-way SYN/SYN-ACK/ACK instead of the simultaneous SYN/SYN/ACK/ACK.