who you going to believe? The generally accepted quotation, which was a true statement at the time, or a Wired article? :-)

a single pi could control upto 28 servos using software and the onboard GPIOs.

That dosn't allow for background software to running, so things will hang and be "not smooth". The robotic arm controller also needs to sending realtime feedback, and that means running a few socket connections, and a bunch of other position monitoring software within the arm controller. All non-blocking.

As I think now, even a PI may be stretching it's power to do all that.

I have a Pi which complains that the processor may not be able to keep up with the process of re-expanding a low-quality video to full-screen. So the Pi still is slightly underpowered, although it is a great device. The price is dropping on 8 core alternatives to the Pi, which have more memory, ethernet ports, and still low power. But Pi's are still good for smaller processing projects, I like them.

All this robotic stuff is probably done best with kernel modules anyways. Instead of running programs, you load a module which does it directly in the kernel.

.... eh it's nice to ponder all that could be done with single-board computers.