good movie, but one major flaw and one explanation about the ending really

Rating: 8/10 (16 July 2010)

hey great movie and really sorry if this contains spoilers, but one question and one comment really (am posting here because IMDb did not verify my account and allow my to reply in the message boards) 1. about the ending - i don't think its that much about the top spinning or falling down. the bigger point is that mr. leonardo did not wait to see whats happening to it. so that means hes more than convinced that this is reality. which should be good enough for us - given that he is the best dude in the dream weaving business.
2. the question - WHY does gravity effect the 2nd level of dreaming (gravity of the van tumbling) whereas it has no effect on the 3rd/4th level of dreaming?? i think that once introduced, the frame of reference point of view should've been kept constant throughout the various levels. or the gravity etc shouldn't have been introduced at all.