There is nothing definite about Melo staying with the Knicks, despite what he may say right now or what 'sources' might say.
It's a long season and things change. Every free agency is different. Had LeBron not got bounced in 2010, he would probably still be with the Cavs.
If Melo has a difficult end to the season, all options are open. From joining up with LeBron to heading to LA to play with the purple & gold. Melo is a talent, there's no arguing against that. But if he sees his window is closing and can't even make it out of the East with the Heat there, who is to say that going back to the Western Conference would be out of the question?
I think it's silly for some of you to sit there and say "He's definitely not coming to the Lakers" because you cannot predict the future. There are positives to coming to the Lakers and there are negatives, just like there are positives for staying with the Knicks as well as the negatives.
The Knicks are in a very particular situation. In 2015, the contracts of Amare, Chandler, and Bargnani come off the books. Melo would be resigning without knowing what that Knicks will do the following season. So their situation is not much different from the Lakers with the difference actually being you KNOW the Lakers will do whatever it takes (within reason) to put a winning product on the court. The same cannot be said for the Knicks.
Either way, Melo could be part of a rebuild when you look at the LA and NY situation, but at least the Lakers start one season earlier.
There will be plenty of other factors in this decision but nothing should be ruled out until he actually signs that new contract.