Apple probably decide by how many they sell. If they sold more year on year with shiny screens than with the old matte screens they will continue to make them with shiny screens. The idea of a glass cover over the screen is good to protect it. It's so anoying when a friend comes round and pokes one of my screens everytime they like what they see on it.
or a easier and cheaper option a earlier iMac , the only option i had as i even on the monitor side matte displays are now rare as hens teeth
dont know why everybody wants these mirrors on their desk , but never mind
i am happy with the iMac core duo 1.83 , and found a samsung sync master 760bf monitor with matte display , ok equipment is years old but i just dont care as long as its not glossy