Many wineries now bottle the same wine with both cork and screw cap. It is due to market expectations, with some believing that a cork is needed for aging the wine ... despite plenty of evidence that most wine ages better with screw cap than with cork. The only benefit of cork is that it allows oxidation which can "burn off" flaws in the wine while screw cap aging is entirely reductive (as it should be). So the best made wines benefit from screw cap, while less well made wines benefit from cork.

Rather ironically screw cap machine for bottling is an expensive investment for a winery, and some of the finest wines are now in screw cap. Grant Burge was mentioned in this thread as using cork -- but the very best Grant Burge wines are exclusively in screw cap, to give the rest of the story and put it into proper perspective. Many restaurants still insist on cork, particularly for expensive bottlings; I suppose it is part of the show for the sommelier. For home use, most wines should be decanted, making the cork vs. screw show irrelevant. In fact decanter shape is more important for some wines