Until atrocious peecees took over the market, workstations were small. And yes, if you had a Sun workstation and you needed additional storage (or even an optical drive) you needed to clutter your desk with external enclosures and thick, difficult to handle SCSI cables.
Of course, in larger installations you relied on centralized storage served through NFS and the users just had the cute little box.
With the new Mac Pro you can go back to that. I guess soon we will see Thunderbolt->10 GbEthernet controllers so that these machines will be able to work with large storage subsystems.
At the same time, the power consumption of a room with several of these Mac Pros, even the necessary air conditioning power for an office, will be greatly reduced.
The deal breaker to move from internal expansion to external is simple: I/O bandwidth and flexibility. In the old times of the Unix workstations, SCSI was the same regardless of being internal or external. When the industry moved to cheaper alternatives such as ATA and SATA, external storage (based on USB or Firewire) was subject to the external bottleneck, so it was important to have internal storage expansion.
But, today? Thunderbolt attached PCIe controllers should be indisguishible from internally attached controllers. There's no penalty beyond a thin cable on your desk.
And the same happens with PCIe peripherals. Even Firewire is much more limited than PCIe, so *internal* PCIe was the obvious choice for many peripherals. Thunderbolt transports PCIe in a way completely transparent to the drivers, as far as I know, so that means there is no penalty.
Does it make sense to keep manufacturing huge and heavy computers? Not at all. People could as well start a petition to Apple for the inclusion of parallel printer, VGA and RS232 ports
