I know people who have older OS versions on their iphones and ipads who can't play Soundcoud. The most recent updates should have cleared that up. It seems to me that maybe that version of Safari isn't playing well with HTML5 which is what soundcloud is built on. The whole idea being that HTML 5 is designed to be played across androids, iphones and supposedly everything else. Anyone with an older browser or who is using IE might experience problems.
You would think that IE would be on their game but in this case not always. I use Chrome and Safari and they seem to be ok. Soundcloud also occasionally updates their servers and things are down for a short while.