Use of articles - varied examples

Following examples are taken from the obituary section in the Economist magazine.


Janet Frame, a chronicler of mental turmoil, died on January 29th, aged 79
Daniel Boorstin, a great amateur, died on February 28th, aged 89
Jose Lopez Portillo y Pacheco, a prodigal president of Mexico, died on February 17th, aged 83
Ahmed yassin, a Hamas leader, died on March 22nd, aged about 66


Marco Pantani, Italy’s favourite cyclist, died on February 14th, aged 34


Lady Virginia Twisleton-Wykeham-Fiennes, organiser of explorers, died on February 20th, aged 56
Eddie Clontz, master of tabloid journalism, died on January 26th, aged 56
Alistair Cooke, smoother of transatlantic tensions, died on March 30th, aged 95

As you can see, the middle section is used to descrive the deceased. Some use an article or some kind of determinor/modifier (am I correct to use the terms?) but some don't.

I would appreciate if someone out there could explain to me why.