Most modern op-amps with such a high bias/offset current are bipolar low noise types that run the input transistors at relatively high current, and do not have particularly low Vos, so it's not much of a concern usually. A +/-200nA input offset current will result in an error of +/-2uV in the Vos reading. With, say +/-10V supplies, and an op-amp that can swing within 2V of the supplies, this circuit will work with offset voltages of up to +/-8mV, which covers most op-amps. A 25uV Vos results in an output voltage of about 25mV in this case.
The gain is chosen so that the output will not saturate even for maximum specified input offset voltage and also such that the open loop gain will not unduly affect the accuracy. R1 is chosen to be very low value to minimize the effects of input bias current. R1 and R2 are chosen to give high gain (but much lower than the open-loop gain) and there is a mirrored pair on the non-inverting input to null out input offset current. Here is one way in the real world to measure input offset voltage, as described in this paper from Analog Devices: You can certainly test a single supply 3V op-amp by applying +/-1.5V supplies which matches my definition. AD skirts the issue by assuming bipolar supplies. For example, a precision amplifier might have an open loop gain of 10^6 so a few volts at the output represents a few uV at the input. It's a bit hazy what the output voltage condition is (you can think of this as the "output offset"), and open-loop gain is so high that it usually doesn't matter. Offset Voltage: The differential voltage which must be applied to the input of an op amp to produce zero output AD defines it thusly in the below-linked paper, but it's not inclusive enough for my liking: You can also think of it as the voltage (assumed that both inputs are within the operating ("common mode") range of the chip) that must be applied differentially to cause the output voltage to go to 0V (bipolar supplies) or perhaps midway between Vdd and GND (single supply). Input offset voltage is the voltage source that would be connected to an input of an ideal op-amp to model the behavior of real op-amp.
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