Opamp output voltage in negative feedback
Unless many things are stated explicitly, all opamp circuit equations for inverting gain, non-inverting gain, active filters, integrators, etc. assume that the input and output signal voltage ranges stay within any particular device's input and output voltage ranges.  For example, an LM741 output stage can get up to only about 2 V below Vcc while a contemporary rail-to-rail opamp with a light output load can get to within 0.1 V of Vcc, but none of this figures into the gain equation.
Note that the voltage rails do not always equal the max signal range.  Many device input stages are designed such that the low value of the input common mode voltage range extends below the device's negative rail.  And, Linear Tech has parts that can handle input voltages way above the positive rail.  As always, read all of the datasheet.