Why is Vcc(-) always grounded in opamp circuits?

[rbruss82]

I've noticed that in every single opamp circuit I've seen for guitar pedals, the Vcc(-) terminal is always grounded and the Vcc(+) terminal gets all +9V.  Why don't we ever send +4.5V and -4.5V to the respective terminals?  Is it just because it's easier because you don't have to build a circuit to split the voltage, or is there a more technical reason?

Also, could you send all -9V to Vcc(-) and ground Vcc(+)?

[Paul Perry (Frostwave)]

Actually, the circuit can't tell where ground (zero volts) is. Unless you arbitrarily choose to call the 'ground' lead to the guitar zero volts (as we normally do).

This may seem merely playing with words, but it will be worth remembering one day, when you are trying to analyse the behavior of a 'strange' circuit.

As it happens, most of the fx that I manufacture have -15 and +15 rails (because, they are based on early analog synth circuits). For these, -Vcc is -15.

[cd]

It's easier to implement the "insert plug in input jack to turn battery on" feature when the opamp is biased to half the supply voltage.