Hummm probably because it is true A RS1 scales up with an amp, but less than a HD650. Let's say I have no headphone amp, a RS1 and a HD650 and I go trying them around at any pre, speaker amp, computer audio card, DAP, whatever; at the end of the day I would buy the RS1 for sure. So, you can live with a RS1 and no amp. If you have not_the_end_of_the_world amp you get 95% out of a RS1. Most of people can live with that. With a HD650, you get 70% and that's the veil, the highs roll off (humm maybe that is for real ) and so on.