Exactly. Also, many pleasure boaters don't get that far out there, especially with the rougher seas this time of year. I've been out there in 20 foot seas.
As someone with a decent amount of experience in commercial aviation, this whole story sounds fishy to me.
First of all, AA621 isn't even a flight out of LAX, nor does it head to Chicago. Its routing is Minneapolis-Dallas-Orange County!
Secondly, when a flight is taking off to the west from LAX (as they nearly do), they are at about three thousand when climbing over Dockweiler Beach. Then when the flight is 5-10 miles over the Pacific, it will turn east. But, the departure patterns out of LAX, depending on traffic are fairly unpredictable. LAX is a well-secured airport, even on off-airport locations, they patrol often, and if there was a missle fired during the day--a lot of people would see it even if the a/c was over the ocean.
AA flights to Chicago are operated with smaller, single-aisle aircraft (below 200 seats). A follower of the religion-of-peace I don't think would waste his missle on a smaller, quickly-ascending target when he has 747s, A340s, and 777s departing all-day from LAX to aim at.