Why is Community Shield repeatedly referred to as "Traditional Curtain Raiser"?

I know Premieship season kicks off the week after this match, but what exactly has this to do with curtains and raising them? Imagine a curtain was actually raised at Wembley before the game!

Traditional Curtain Raiser is indeed a daft title if you think about it literally. Its just one of those silly things tv commentators say, along with:-

"It's a big ask"
"Wonderful ball"
"Shades of 1966"

I was not that impressed with Chelsea yesterday, and less impressed with Jose Mourinho who again refused to shake hands of his opponent.

One thing that interested me at Charity Shield match yesterday was the 2 teams sub benches - one was far superior than the other, and may well be significant as a long season pans out.

CHE - Hilario, Mancienne, Mikel, Bridge, Kalou, Wright-Philips, Diarra

LIV - Dudek, Hyypia, Gerrard, Alonso, Aurelio, Sinama-Pongolle, Bellamy.

OK, Gerrard and Bellamy will be first picks, and Joe Cole is missing (and Ashley Cole I guess!), but the Chelsea bench was very young.
Are they good enough for Premiership title winners? Cech was badly missed too and would have saved that long range shot.