It's pretty simple. I think the reason Apple is switching to same day pre-orders is so that they don't have quite as many people taking down their servers. When they waited three days before the pre-order, it gave EVERYONE who wanted to pre-order a heads up of when it would happen three days in advance. With the iPad 3, some people probably didn't even know it was available until later that night after work. It took me maybe 45 minutes to get the iPad 3, but I remember the iPhone 4 took like 12 hours.