I think I remember reading somewhere that the 9V is really just VIN, and they renamed it in a later version.
That is correct. To be really accurate the 'old' 9v was not really 9vdc, but rather whatever the voltage at the external power connector is minus the voltage drop across the polarity protection diode. So if you were plugging a 12vdc power module into the external power connector then the 'old 9v' pin and the 'new Vin pin would both see about 11.4vdc. The current available on this pin is limited to the current capacity of the external power module and/or the current rating of the protection diode, whichever is less.
You can also provide power to the board by inputting a voltage (8-15vdc, the lower the better) to the Vin pin (or the old 9v pin) rather then through the external power connector. Both paths go to the input of the on-board +5vdc voltage regulator.
That older board photo is of the Arduino NG or Arduino Extreme v2 from the photos and schematics shown here:
( http://arduino.cc/en/Main/Boards ) Note the 4 pin power connector (+5,gnd,gnd, 9v) Vs the 6 pin power connector on newer boards (reset, 3.3v, 5v, gnd, gnd, Vin)
Lefty