The new has a fraction of the chassis materials of the old.
The new has a fraction of the components of the old (no CD, HD, cables and a single cooling fan).
The new has a smaller foot print of the old thereby Apple will save on shipping to stores/warehouse and be able to stock more units in stores.
The new should have a fraction of the assembly labor time of the old.
The new has an inexpensively produced design, the beer can shell.
The new should be less expensive to update compared to the old because it use three small boards instead of one large board.
The new will have practically no warranty repair of the old because of no mechanical drives.
The new should sell for much less than the old considering. It makes me believe because of its small design that Apple may be thinking of eventually replacing the Mac Mini and even the iMac with this Mac Pro if they price it right. It will reduce their product line but instead offer consumers a powerful yet affordable unit that they can expanded and be a computer, server, media server etc. If Apple goes the other way and sells it for more than the old units it will sell few and make people turn to the hackintosh community.