That's correct. The 12AV7 is a driver tube, with specs that fall between the 12AT7 and the 12AU7. It never got used much because it was the "middle child." The 12AU7's plate impedance makes it more useful for good impedance match when driving small output transformers, as with a 1-watt guitar amp. You can do a neat little push-pull amp with it.
Here's an example:
http://www.diyguitarist.com/GuitarAmps/FireFly.htm