
If you take a look at the footage of the explosion, Jin was standing at the end of the boat where the heliocopter had taken off from. The explosion came from the center of the boat and tore it in half. From where Jin was standing, he could have easily jumped (or more likely, blown into the water) as you can see. Also, if were to take this as the heliocopters view of the explosion, that's pretty far away to see if there are survivors.
Additionally, the writers of Lost rarely seem to do anything without a purpose, and therefore there must be a reason that Daniel was on his way to the boat in the dingy. Daniel is the scientist who seems to know the most about the time and space displacement that the island seems to experience. You are correct, though, his boat was full and that there would logically be other survivors, but from a cinematic perspective, Jin is the only named character other than Daniel, so if they develop some story of how he gets on the boat and connects with Daniel, that will then provide an additional story line for us to follow for some period of time.
Of course, Daniel Dae Kim (Jin) did get a DUI recently in HI, and we all know what happens to people when they have runins with the law in HI. Michele Rodriguez for instance.
Ah...wait...epiphony...Sun blames Jack (presumably, we know there are two, the other being Paik) because he was their leader and ordered them to fly away instead of saving Jin or looking for his remains. And it's Jack's job now to convince all of those from the island to return to the island. If Sun hates Jack for the death of her husband, she would never return to the island. And since he is supposed to be dead, Jin could never live in the real world openly with Sun, so what if Jin survives and Jack reunites them, I think that Sun would return to the island with everyone else. Wow, things are coming together now. I'm going to send in my application to be a lost writer.