Why Or'd Vcc with backup battery output shorted battery life?

[mackrackit]

Vss and Vdd pins are not necessary or can be omitted?

No, I am saying that it can.
Say you have a MCU with an I/O sourced to different power supplies. If the I/O is high and the power is cut to the MCU the MCU will not be able to reset. The voltage on the I/O will keep the MCU running or in a near run state. The I/O can even be a RS232 input.

For a test, have the MCU keep a LED high (lighted), apply 5 volts to an input. Turn the power off to the MCU while keeping the input at 5 volts. Look at the LED.

[Heckler]

Vss and Vdd pins are not necessary or can be omitted?

YEP!! you can power PIC's through the I/O pins... anyway take a look here...
http://www.t4f.org/en/projects/open-rfid-tag/57

I would never have thought it possible... I am sure there are current limitations, though.

I ran across this on one of my favorite web sites... www.hackaday.com