Yeah, there's some conflicting info there. From the tech specs:

10/100BASE-T Ethernet WAN port Yes
10/100BASE-T Ethernet LAN port No

I don't get it. The only difference I can think of between a LAN and WAN port is that a WAN port would do NAT? (I wish they'd spell it out instead of implying it.) So even if that's the case, it can just do NAT against an already NATted address. Inefficient, but it ought to work.

And what's the deal with this extender-only talk? I thought one of its features was that you could take it with you because it's so small. If you also need an Airport to make it do anything useful, that seems like false advertising.

Basicially it's like the old Graphite Airport I had. It has one ethernet port. That port can do local ethernet bridging, or talk to a cable modem and NAT the connection. It however can't do both at the same time, since it only had one ethernet port. The advantage of the Airport Express in theory is that with the range extension, it could be used to do wired-wireless-wired if you have an Airport elsewhere in the house. The old Airport stations would never talk to another base station, just clients.

Newer Airports began shipping with "LAN" and "WAN" ports. Thus, cable modem if in use always goes into WAN, and local devices if used always go into LAN.

Bitt. It can do Airport range extension OR be it's own base station on the go. That way, it sees use at home on existing Airport networks, and is useful on the road.