I was talking to a MA at my local MAC store yesterday about the limited quantities they get in for these collections, and she had an interesting explanation. She said that the number of each product that a store gets is greatly based on how similar products have sold in the past at that location. For example, at this location they received about a dozen Unconventional blushes to sell, but only 2 or 3 Passionately Tempted blushes (with one of each blush being made into a tester). Bold blushes don't generally sell well at that location, but lighter shades do, hence the unbalanced distribution. At locations where more customers are into brighter, bolder blushes, more Passionately Tempted will be available.
I still think sending only 2 or 3 of a limited edition product to a store is borderline insanity, but I found this information interesting anyway!