What is he claiming to be the default there? WinXP is capable of it, though it may not always default to a bridged configuration. Wouldn't be much point to the "Bridge Connections" menu in Network Connections if it wasn't possible.

All you do is select two network controllers (control-click) and then select the Bridge menu item. It automatically bridges them.
All this does is make the extra port act like a "hub" port, and your computer becomes a very expensive repeater, passing the traffic from the bridged port to the external port directly, rather than processing it through Internet Connection Sharing. It'll still watch for normal network traffic like MS file sharing, but it will also repeat the traffic to the external port (presumably being used for Internet access).
Can't imagine why anyone would want to set it up that way. A real 8-port hub can be had for as low as 4 dollars after rebates, and all bridging will do is slow down the main computer (and of course, you still need a real hub to connect more than one computer to the main one, unless you install several NICs).
The only conceivable reason for this would be if the ISP provided an internal PCI DSL/cable modem rather than an external modem, but in that case, you're not likely to be getting more than one IP with the service, and only one computer will have an IP and the others won't work at all. That's what Internet Connection Sharing is meant for.