I just got a 360 "jasper" Arcade from Blockbuster, the nice lady there let me look at the box first, on the front of the box it says "256 Memory" (it's built in) not "256 Memory UNIT". Also you can see the unit is amp rated at 12.1a (jasper) not 14.2a (falcon) by looking through the hole in the end of the box which lets you see the actual unit's serial code without opening the box seals. This is at the bottom left corner just barely visible. I'm guessing as Amazon include the words "256MB Memory Unit" in the product description it's still the older "falcon" chipset box they're shipping?
I just purchased an Xbox 360 Arcade a week ago from Amazon, and it does seem to be the older Falcon console they're selling, yes. Or at least it came with a memory card, as opposed to having the memory built in.