For me it's because a riff.
:26 seconds into the e.p version the riff has picking at the end and on all parts, on the demo version that same riffs comes back in around 1:40 without the picking and the chord is just sustained being held out(comes in a third time the same where in the beginning has muted picking) and it sounds so cool and actually gives the song more variation because it's the same riff just played different where on the e.p it's the same riff all 3 times. I guess this is the best way I can explain it,