The memory as its soldered onto the logic board, and not end user upgradeable or replaceable.
It uses proprietary SSD Flash Memory, so you can’t buy third parts cheaper if your wanting to expand the storage. At least not for a while.
Also, make sure you purchase AppleCare with this laptop. The Retina display cannot be removed/replaced from the top lid of the computer and the battery is glued in place. iFixIt rated this laptop 1 for 10 for repairabilty.
I don’t think this info diminishes how revolutionary this laptop is just don’t think your going to be doing a lot of work on this yourself or that a warranty isn’t necessary.