I guess I'd argue that "Anarchy in the UK" and "God Save the Queen" are "iconic" songs even if they're not as big hits as some of the other artists'. They're instant signifiers of a time and place in a way that "Blue Monday" isn't. Also, I think the Pistols pass the iconic cover test.
To me, Waits is the most obvious one on this list who *shouldn't* be here. Never particularly big and not really important (I'd struggle to name an artist he obviously influenced).