Pizza boxes were smaller than 2U servers, which were more space-efficient than towers, all of which, even the pizzas and the blades showed us not only that horizontal scaling of compute power was much different than vertical scaling, it took up a hell of a lot more room.
HP and Rackable are among the server makers trying yet another version of the "cookie sheet," a form-factor invented, almost accidentally, by Google when it decided to build its own servers in as dense and openly ventilated a set of racks as it could.
HP is now putting three GPUs in its latest version of the design, the better to fulfill the mission of cloud computing and virtual desktops. Regular pizza boxes and blades and shoeboxes and whatever else is in your filthy old data center only needed engine power. All a non-cloud, non-virtualized server had to do was crunch numbers, serve files, save potentially litigable email exchanges in places that weren't easy to find, and break down when the quarter and the books are closing and Accounting has that serial-killer look in its eye.
Running virtual machines, especially virtual desktops, means creating and transmitting not only data, but pictures of the OS or application across the network so a user can see it run just as fast as if it were running on his or her aged laptop with the banged-up corners and keys that keep falling off.
So, what data centers need now is more servers to run the VMs, more density to fit them in the same data center, more cooling to keep the data center staff from drying up like jellyfish in a sauna, and the kind of graphics power any 14-year-old gamer would kill for, and no 54-year-old CFO would approve without far more explanation about why the data center needs better graphics than you're willing to give or the executive staff is willing to hear.