While I for one have felt that something was funny about that crash since that day (reports of a streaking light toward the plane, as I recall), allowing Osama et al to start claiming credit for all unsolved events gives them more creditability and power in the terrorist world.
Terrorist groups have always been all very careful about which actions they claim credit for and which they deny. The IRA are known to use specific coded names to let others know they truly did do a thing.
If they did do it and specific evidence can be made linking them to it, then by all means punish them for it. If we allow them to take credit for every unsolved tragedy in the world, then they gain in their ability to inflict "TERROR" on the world. If we let them do take credit where credit is not due, then we empower them.
On the other hand, if we refuse to accept their claims without proof, then we call their bluff. We tell them, "hey, we don't think you're all that powerful."
Letting Al Qaeda take credit for something they did not due only furthers their cause. It's a twisted thought, but this could give them credibility in certain parts of the world.
The U.S. is big and we're tough, but we cannot be all places all time. Let's not fuel the fire.
I've always thought this could be the 1st shoe bomber.