It's simple. From a certain point in his career onwards, Speilberg owns his movies, first under the
Amblin' banner then
Dreamworks.
Close Encounters of the Third Kind is one of the earlier titles that is not owned by him. It is owned by Sony/Columbia, hence the reason it is the only title available so far.
Of course Bill Hunt
et al have tried desperately to spin this as "Steven Speilberg supports Blu-Ray." All that the press release from Paramount says is that his films are not exclusive to either format, nothing more.
I would interpret that as SS hedging his bets, like Lucas, and waiting for a winner to emerge in the format war and for a large customer base to become established for HD-DVD - oops, I mean whatever the winning format is

, before deciding to release his movies on the format.