I want the new MacBook Pro 17" ($2799). Looking into the ADC, I can pay $499 for a Select membership, which includes one hardware purchase per year. That would make the MBPro $2239 (figuring 20% off), which is more than a $500 savings. Why would I not do this? Do I get to make a 20% off purchase every year for a one-time payment of $499? What is the catch?