I hate to tell you this, but I think Apple's feeding you a line of BS.
If FedEx's tracking page says it's being delivered on the 28th, then I would fully expect it on the 28th. The person you spoke with may be correct in that if you order an iPad *today* they'll ship it out with overnight shipping and you'll get it tomorrow, but if you ordered it a couple days ago and they shipped it ground, then, well, you may be screwed. I would trust FedEx's tracking page over some Apple phone rep. They're the ones delivering it and they know better than anyone else the type of service it was shipped with and how long it will take, and I've always found the estimated delivery dates of both FedEx and UPS to be spot on.