"Long story short: if the president went on TV and flatly stated something as important as this in terms as unambiguous as he did, it's because it's true."
This is the principle reason anyone believes Osama is dead. And it is such utter nonsense I find it hard to believe it appears to be a majority opinion!
Here's a few of the main possibilities:
1. Obama did send troops to kill Osama, they did so, the story is all true. That would be great if and only if they could produce incontrovertible evidence that the guy they shot was Osama. If for any reason they cannot produce the evidence, they are in massive international trouble (unless they can brainwash patriots and fools into believing they just wouldn't lie about something like that).
2. Osama was killed years ago, appearances since have been by doubles and they just killed one of them. It was politicially convenient to have the 'hunting Osama' excuse to do otherwise inexcusable things in other countries (like mounting unannounced military operations in civilian areas of foreign countries and generally exerting massive political force, gaining power over critical arab regions).
3. Osama got away, his followers remained loyal, the military operation was fake (say, they conveniently killed a rogue double agent or whatever and pretended it was Osama) because Obama wanted the popularity for the elections and wanted to change political stance (sacrificing the 'Osama hunt' excuse).
Obviously the truth is likely some variation of the above, somewhere between 1 and 2 or 2 and 3 perhaps. For all those spanners who said "but then Osama could just release an 'Im alive' video so Obama wouldn't risk it", any intelligent terrorist will do this with some reasonable look-alike over a poor quality satellite video if Osama really was dead. So if one pops up, and the government still doesn't want the hunt to be on, they will claim its a fake and everyone will believe him because its the US government. They (US) may even release an obvious fake themselves if they want to incite unrest.
DNA evidence is a minimum, much evidence needs to be provided. This could be linked to family members, remember the US has a long history of working with Osama and his family and hosting them as diplomats. If they cannot produce enough evidence to prove it to the public, then they have no right or reason to claim or believe themselves that Osama is indeed dead.
My gut feeling is that he has been dead for a while, no-one's quite sure when or how he was killed and the US seized on this to create the great 'Osama hunt excuse' which has been an extraordinarily powerful tool for the US to leverage massive extra control and freedom in the international stage.
The terrorist threat will never be over until the countries principally benefiting from its existence decide they are going to stop it. If the US feels it is perfectly safe and happy, it will only ever be when it has near-total control over every other country and the lion's share of every resource on the planet. Who wants to take bets that in our life times China becomes the new Cold-War USSR, possibly linking triad organised crime as a form of terrorism and linking them to government? Whatever is expedient at the time they want an excuse I guess. This is not mindless conspiracy, just expecting the pattern of behaviour shown by US government and war cabinet since (pre/post?) WW1, which has not yet been broken, to continue as usual.
