Why the +/- 5 V Power Supply?

The +/- 5 Volts is the power supply requirements of the MAX 275 that we use. We considering making the output supply swing +/- 10 V, but that would raise the cost per unit to have +/- 5 V and +/- 10 V power supplies. There were some other limitations. We did consider these before choosing to keep everything simpler with a +/- 5 V power supply.