I totally agree. Considering how frictionless much of the purchase procedure is, it seems odd that you cannot buy an app unless you are in the position to download it at that time. They could just be waiting on the device like they would be if bought on another device with the same account. Just have a warning that you cannot download at this time, and a choice of if to go ahead. The same goes for buying something that isn't suited to the device you are purchasing on. I have tried to buy iPad apps when I only have my iPhone with me, so that it is waiting for me when I next use my iPad. Instead I often forget about the purchase.
