There was a 6 month long viral web campaign which explained all this. The company the main character works for (and is moving to Japan for) makes a soft drink called Slusho (also seen in Lost) which has some strange properties - like Reb Bull only 10 times. The theory is that the 'special ingredient' in the drink is extracted from the sea bed by a series of deep sea drilling platforms located around the world. One of these in mid Atlantic was destroyed a short time before the start of the film. Again, the theory is that the monster lives in the abyss and it or it's whole species has grown huge as a result of the ingredient. There is a link there with the parasites and what happens if you get bitten by one. There's a manga comic which expalins some of this in more detail and has a bit suggesting that an oil tanker (maybe the capsized one in NY harbour) towed a large object away form a platform. There are also some pictures of the US Navy engaging something in the waters off NY a few days before the start of the film, and getting their arses kicked.
Now, the thing seen falling into the sea off Coney Island is a Japanses Govt satellite. The drilling company also has deep sea surveillance satellites and one of these is used to find the ditched satelite. Somehow that links in to the start of events, but I'm not sure how. it could be that in looking for the satellite the company finRAB a rich source oif their drink ingredient and when they go to look for it they disturb the monster. The problem there is that the ditched satellite is clearly seen hitting the sea in the video at the end of the film and can therefore be no more than a few miles off the coast - hardly the ocean abyss or a likely home for a deep sea monster.
I hope that clears things up.
As for the DVD, the extras are great for the 'making of' side, but have very little on the whole background of the story or how the viral campaign was put together which is something I'm really interested in.
