I guess you are aware of the power consumptions and computation factors of both of the platforms...
The PC is designed to compromise the power consumption and give you the best possible performance by the chip supporting 24bit 192khz
whereas the phones are not given the high end chips because of the limited power within the battery.
If you want the PC quality you will have to charge your phone like forever to get that clearity level..
..
And about the iphone and s4, they are the flagships of the companies. They want you to see the difference with a little difference of technical units as well as the headphones.. They have slightly more amplified signal to get that sound.
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Though i heard of a chip designed recently for mobile support that'll be able to produce 192khz but no company can use it due to high power consumption !