I don't want to fuel the discussion, but I think there is a subtle difference between the alpha/beta access and "physical" rewards which nobody has pointed out so far (unless I am mistaken):

"Phyiscal goods" (by which I also mean a digital distribution of the game etc.) have a life period of many years. Everyone knows that the prices for physical goods will drop eventually and that sometime they also will go on sale. So, everyone makes a decision, whether to pay the full price for the goods now and use them immediately after release or to wait for another two years before purchasing them for just 1/10 of the full price.

Alpha/beta access is in contrast a once-in-a-lifetime event for the game. So, it is kind of weird to put them on sale before the event has even taken place.

Compare it to a film premiere and a DVD release. If I buy a DVD on the first day of its release, I know I will get it much cheaper one year later. If I pay a few hundreds dollars to go to a film premiere, then I expect that the price remains constant until the very day of the event. I pay for the possibility to mingle with the stars, for the whole atmosphere and for the awareness to belong to the "chosen circle" of people who go to the premiere. If, however, it is customary that the premiere tickets always drop in price 1 week before the event and EVERYONE can buy them, then I am likely to be annoyed that I paid so much money for something which is now available at half price and will never bye any premiere tickets anymore at full price but wait until they are offered for cheaper.