Has anyone ever asked Ron Sutherland what he thinks the sonic difference is between his SMPS and LPS versions? Ron is a brilliant engineer and I find it hard to believe he overlooked this in the original designs. He went from batteries to SMPS, bypassing LPS altogether in the beginning. That looks like a very well-considered decision to me.
My thought is that he is producing LPS versions purely because of customer demand, not because he thinks it makes for an inherently better product. He worked hard to get ripple down to less than 1 microvolt on the original 20/20, per his 2011 Stereophile interview - that's an incredible amount of power supply filtration.