When Brian Porter (Susan’s husband) visits Michael after Susan has died he gives him return tickets between Sydney and New York. This must mean that Michael and Walt would have needed a connecting flight between Los Angeles and New York, but thats not the important bit. The important bit is that this indicates that Michael lives in New York…or at least he did.
Remember the newspaper death notice that Jack reads in the season 3 finale, I’m pretty sure it mentions that the deceased was found
in a New York loft in Los Angeles but was from New York. And according to some sources the article also says that the deceased left behind a teenage son. Walt is 10 on the island (in 2004), the flash forward takes place in 2007 making Walt 13 and therefore a teenager.
A couple of thing explain why no one was at the funeral, since it appears from the article that the deceased (if it is Michael) has changed there name, and as far as we know Michael doesn’t seem to have a lot of family around. Some have also mentioned that the funeral parlor appeared to be a in an African-American neighbourhood, also points to Michael.
It also then makes sense that Jack is upset, its not because he was close to Michael (remember when asked ‘friend or family’ he responded ‘neither’) but because Michael was quite possibly one of his last remaining links back to the island. Since we know that Michael will be reappearing in season 4, it would make sense that Jack would believe that he knows how to get to the island…just as Jack is desperate to do. This also explains why it is someone that Kate wouldn’t visit, theres a fairly good chance she hasn’t forgiven him for murdering Ana-Lucia and Libby or something else that happens after he returns…