Apple has a "feature page" on its site regarding the iPhone 4's antenna; the video was posted both there and on YouTube. Apple's video purports to show that holding the Droid X signal bars dropping from 3 to zero.
Despite all the claims by Apple, manufacturers and others have noted that a) Apple is the only manufacturer with an external antenna system, b) other antennas are located in such a way as to make a "death grip" require contortions, and c) the "death grip" on the iPhone really requires just a finger to bridge the gap between two antennas in its external antenna system.
We were also unable to reproduce Apple's demo using a "natural" grip on the Droid X, using two separate devices in the same location.
We expect Motorola to fire back about this. The Droid X sold out and became backordered quickly after its July 15th release, despite assurances by Verizon that they had plenty of stock.