> Wait a sec - so you're saying there are devices which actually violate 
> Ohm's law?

Yes, more exactly, there are devices which do not have constant 
resistance/impedance.

> Uh... so have it always connected to one rail, but through such a high 
> resistance that the rail can't affect it?
>
> Well, you're the one with the engineering degree, but it *still* doesn't 
> make any sense to me...

Maybe it would help if you imagined that inside the IC there is a big 
resistor (eg 1Mohm) connecting the input to one of the supply rails (but you 
don't know which one).  In order to ensure this resistor cannot affect the 
input voltage, you need to make sure the input is always connected to the 
voltage you want through a smaller resistor (electricity likes the lowest 
resistance path!).

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