Tim,
The input stage on an amp is not an output stage. Output stages have to drive a speaker, so you would not want current limiting. The input stage is just an op amp. Most integrated circuit op amps cannot drive over 100ma. They are using a discrete op amp that can drive 250ma. In fact, the circuit will never need much current at all. As all that will come out of it is a few volts and driving maybe 5K load. They are basically bragging about their discrete op amp. The spec has very little to do with sound. You could have a circuit that could only drive 50ma that could sound better.