The arduino is just a computer on a chip.
It can be very clever. But that clever bit is the code. The computer code that is the increadibly complex part of a wheelchair controller.
For eg, on our robioteq controllers the clever part is the bit that lenny wrote. The script that allows the controller to work correctly. On its own, its useless. With this, its great.
http://www.wheelchairdriver.com/BM3-con ... Script.txtScroll. This is in addition to the roboteq's own software.
The rest of the roboteq is a chip like the arduino, and a LOT of very complex and expensive components to handle large currents and be safe and reliable. That allows the thing to have a lot of power, and a lot of flexibility reliably.