Mao never left the post of the chairmanship of the central committe before his death. It was Deng who started this absurd tradition and Jiang was just plain power greedy to follow Deng's footstep.
By not giving up his position in 中央军事委员会, Hu violates CCP's principle of controlling the military under the party's leadership. Imagine Hu becoming more powerful than the boss of the party simply because he is the Chairman of the 中央军事委员会. I guess he is not the first one, but I certainly hope the last.
On the second thought, the military leadership should be appointed by the new boss, not the departing one. This is so routine everywhere else. Or better yet the military commands stay put and professional regardless of the changing gourds at the top.
中央军事委员会 should be abolished as there is already a 国家 军事委员会.