i reckon i can beat that on my gary fisher, been likie that since i bought it circa 2000 and still holding strong - it is my daily ride. as ^^^^ said, manufacturer's err on the side of caution.
having said that, i have had 2 posts snap - use post - thin flimsy thing used with a shim, as per original spec, that was replaced by a supposedly unbreaka le nad very expensive control techj post that went the same way. it can be nasty and dangerous when a post snaps - the first thing you know about it is you are sitting in the ground wondering why you are not on the bike, the jagged remains of the post can gouge your leg, can potentiall by quite nasty as there is big artery there.