There's no a priori reason why any recording medium needs to have a flat response curve, so long as the curve is known so it can be reversed. The reason for the

There's no a priori reason why any recording medium needs to have a flat response curve, so long as the curve is known so it can be reversed. The reason for the RIAA curve is that most sound has an inverse relationship between amplitude and frequency. The RIAA recording curve limits the overall amplitude of the groove, allowing for better management of dynamic range and distortion in the cutting and playback processes. The slight lumps in the curve are a concession to practical filter technology of the 1950s. Other analog broadcast and recording media have similar curves, called pre- and de-emphasis. Digital doesn't need it because it has effectively zero distortion, and dynamic range to spare. An advantage of vinyl is that there's a physical deliverable, making it possible to monetize it. I think that's why a lot of indie bands use vinyl.