I just don't see why anyone need to put up with two changes between NRT and the hotel (Keisei/NEX+Yamanote+walk/cab) if they can afford a shortish cab ride, especially after usually very long flights.

NEX to Shinagawa or Shibuya, then a 2500 yen cab ride to the Westin. (A little less from Shibuya, but it is a much more confusing station, with a long walk to the cab stand, and it involves some backtracking).