Not sure why Obama or the administration would lie about OBL's death. The consequences would be catastrophic to him and his administration. Which leads to ...
If OBL had been dead since 2001, then not sure why GWB wouldn't have mentioned it, especially when his approval ratings were in the toilet towards the end of his presidency.
I also approve of his body being dumped in the ocean regardless of whether Islamic ritual was followed. Where exactly would OBL be buried? If in the US or any other location accessible to US citizens, then you invite grave desecration, unless you want to spend tax money to guard the gravesite (which no one would ever approve). If in the Middle East, you create a "Mecca"-like site for Muslim terrorists (not exactly appealing to our own US interests). Perhaps an unmarked grave in an unknown location? Then you invite a whole host of grave-seekers, and perhaps sooner or later the location will be revealed; plus, the info's going to be recorded somewhere.