Any Home Team can Win in Home conditions like How India Manipulated & Doctored the Wickets to suit Spinners from Ball 1.
South Africa Lost to England, as they were Psychologically wrecked after losing to India in such a Brutal manner.
Also SA lost Dale Steyn & Vernon Philander to injuries and their Pace attack is not so good without them as how England's is at the moment. ICC should look and introspect into every details & then declare who is No. 1.
In this case England deserve to be Number 1 after they beat South Africa 2-1 in their own den.