There are two other scenarios to consider. Many aren't able to monitor the bidding site in real time and put in a max bid. They only put that in on one of the packages for they only need one of the packages offered. If I put in 10k points on all three that are offered for example, i could win all of them when I only need 1. Thus you can sometimes see one of the packages on offer, usually the first one, go for a higher price because of this. If I only need one package I will set my autobid to only one of the packages on offer for just this reason.
The other reason the first package would go high is if someone needs MORE THAN 1 package. They have to get the first one to make the others possible thus they will push it as high as needed. If you don't get that first one you are screwed.
So the above scenarios can and do happen, however I would never question the integrity of the spg moments system. They are a very nice perk to the spg program and I value those I have had the pleasure of winning. First class experiences all the way. ^