Yes I consider Kallis as one of the most complete Cricketer to graced the game in Modern Era. But Unlike in India, other countries are professional in Selection and players are retained on Merit, be it Kallis, Ponting, Steve Waugh, etc. Being 38 yrs and reduced run scoring it was getting difficult for CSA selectors to continue to persist with him.
Also I too feel it would be difficult for Kallis to play 2015 WC in Australia, as the grounds are big and it requires highest levels of fitness. Remember Walsh was dropped from West Indies team in 1992 World Cup just B'cos he was not fit to throw the ball, even though he was legendary bowler and even India paid the price of by including Ravu Shastri, Srikkant, and Kapil Dev in the 1992 World Cup who had past there prime !!!