I found the whole premise of going 3 dreams 'deep' to plant an idea uninteresting and unbelievable I guess. It's also full of small plot inconsistencies which annoy me;
Saito just takes it for granted they succesfully planted the idea? he was unconcious/dead when Fischer got the new will.
And why was Saito so bloody old.
And if they could just kill themselves at the limbo level to wake up why not do that instead of all the over elaborate kick things
i think saito said, he would honour the agreement regardless, somewhere in the film, when they start heading into trouble, or after he gets shot.
saito was so old because thats how it works, i cant remember the specific timing so i made this up to show:
1st level - 1 second in real world = 3 minutes
2nd level - 1 second in real world = 3 hours
3rd level - 1 second in real world = 3 days
saito's level (limbo) - 1 second in real world = 3 years
saito was the first to go into the limbo level, therefore for every second the people stayed on level 3, he aged 3 years in limbo because thats how long he spent in there.
di caprio managed to wake himself and his wife up the first time they were in limbo by killing themselves, but they had spent like 70 years in limbo (they grew old together). you cannot wake up from a dream when you are under sedation.
think about it in real life, if a doctor sedates you for an operation, you are put to sleep. no matter what happens you will not wake up until the sedative has wore off. therefore they must still be sedated in the limbo level and the air hostess on the plane must have to give them something at a specific time (1 second before the "jump") in order to un-sedate them or its a timed sedative which wears off at that time.
therefore they cannot kill themselves until they know for sure the sedative has woren off. they know it hasn't because saito goes into limbo instead of waking up.
any more questions?