When you have a noise "digital side" in close physical proximity to the analog "side", perhaps in a mobile device, then the "analog and digital sides" definitely do mix. It's entirely possible that these cards make an audible difference in various playback devices ... doesn't seem too likely but the effect that Sony is trying to reduce is similar to how placing a cell phone next to some playback devices induces audible differences.
Plus, the best way to deal with noise is to prevent it in the first place!, not attempt to filter it out (I assume that's what you mean by "dealt with") "at the analog end of the audio circuit."