The were the first ones to make it the standard controller for their system and have that system become a success.
Sony may very well have been working on motion control in 2004 but then either Nintendo has a much more efficient R+D process or it's reasonable to expect that they were working on their solution even before that.
Furthermore there is nothing in that demo to suggest that Sony had any intention of making that controller the default for Sony systems or anything more than a novelty to be used in some games. Any comments from Sony PR would suggest they had no faith in motion control becoming an industry-wide standard or perhaps they were just trying to convince people not to go with Nintendo's version and give them time to complete and market their own solution.
Even if they were developed entirely independently and Sony had always intended on pushing motion controls, the similarity in form factor with the Wii-mote and the very late arrival to the market is just going to make it look like they copied the Wii-mote in the eyes of most consumers.
edit: the NES wasn't main stream?