Or a better question is "Do corks need to be made of cork?"
When I was a kid I drank some really, really bad wines: the ones which came with screw tops. I'd mix the wine with some carbonated beverage and create some God-awful concoction that was fizzy, fruity and would get me a slight buzz. What more could an 18 year old (legal drinking age at the time) desire?
A screw top is a superior way to seal a bottle. Cork is an agricultural product with a wide degree of variability in production. A plastic and aluminum seal is virtually foolproof.
The curiosity in this matter is that innovation usually originates with the market leaders, but in this case innovation began with high-volume, low-quality products. And perhaps that is the entire issue. There is reluctance from the buying public to embrace a technology that was not originated with the high end products.
Perhaps it is more basic: premium wineries are like lemmings. Not enough have yet lept off the cliff.
I see screw top enclosures on the top of small brands and I think that is how it will continue for some time. Wineries without a lot of cash and seeking to extend their brand will be practical and efficient with less concern about the loss of the uncorking ceremony.
Think of Steve Martin (the overly snooty wine captain) asking Ms. Piggy in the first Muppett Movie: "Would you like to smell the cap?"