I recently discovered an emulator online of my first 8-bit computer (the Compucolor II), and I was amazed at how simple it was to use (draw graphics to the screen, read from the keyboard or disk etc). Whilst you have to write all of the high-level processing yourself, the actual low-level magic is right there at your fingertips. Want to set a pin on the serial port - not a problem, the I/O is memory mapped, and the address you need is in a table in the 100 page manual that came with the computer. Done! Compare that with today's environments - find out the API needed to access a serial port pin (if it even exists!), pull in the system headers and libraries necessary (after figuring out which are used!), modify your build system to use them, and then run.
The beauty of Arduino is that it takes you back to that bare metal simplicity. It makes interfacing to the real world very easy. If you want to run a webserver it's probably not the best choice, but if you want to switch off your washing machine because a sensor has detected that a pool of water has formed on your kitchen floor, Arduino is so much more accessible for an amateur. I really don't understand where the manufacturers are going with these boards...