Everyone complaining with "but stairstepping" fails to recognize that the final stage of a DAC is a reconstruction filter. The steps are gone after that filter is applied. You aren't analyzing the full DAC performance if you look in front of the filter. This is most dramatic in class-D amplifiers where the raw waveform feeding into the speakers is square wave hash that gets filtered out by the speakers themselves.
The filters do linear interpolation between samples. This bridges some shortcomings of a sample rate too low to capture complex waveform at high frequency, but it's not a silver bullet.
