I don't think this is as terrible as most make it seem. You know the tablet is 3G ready. You also know it can be upgraded to 4G with stipulations (sending it in, not having it for 6 days). If you don't want to take advantage of the 4G you don't have to, and you don't have to go through the hassle of sending it in.
Seems reasonable to me, you have choices, plus, my May your XOOM fever will be under control, so you will likely be ok without having it for a week.