Siren: Blood Curse in hopes of a Blu-ray release? If you are in the US, don't bother. Sony has spoken to MTV Multiplayer, reiterating that there are no plans for a North American release on of Siren in disc form "at this time." The Sony representative reminds us that "you are able to delete and then re-download episodes since the purchase is linked to your PSN account. The developers kept this functionality in mind knowing that the episodes were fairly beefy."
MTV speculates that Sony may simply be testing the waters in terms of Siren's sales before releasing a retail version. Either way, if you really want the game on Blu-ray, you can always just import it from Europe.