Well, consider it this way. If they detonated the bomb, they would never have shown up on the island, thus, they never would've detonated the bomb, a paradox. Maybe the only way to resolve it is to have two simultaneous realities. It reminds me of what happens to Jake and Roland in the Dark Tower series. I think that was book two, The Drawing of the Three, where they both were seeing two realities at once.
Anyway, the thing about the airplane version is that it's not exactly the same as it was when they actually first took their flight. Desmond wasn't on the plane originally, but somehow he was in this new version, at least temporarily(?), and Shannon (Boone's stepsister) was on the plane originally, but in the new version, didn't end up coming back with him. So we know that this changed timeline involves more differences than just not crashing on the island. Whatever alternate path they're on, the repercussions of it extend out into the world at large, and have changed the bigger picture in ways we will probably only understand as the season progresses.
Also, the two realities are offset by at least a few months, if not three years, since the hatch is destroyed, but was there any solid evidence for what year it was on the island?
