- his extruder has a shaft encoder to control the speed precisely
- he has temperature control to +/- 3C
- he doesn't have any comms delays (I don't know the architecture well enough to know exactly what he means here)
- he runs his head faster so as to stretch the filament down to 0.5mm.
- careful choice of printing material
Within just a year or two, RepRap will be much further along in terms of both quality and ease of use, and it will be affordable for small clubs in high schools and colleges all over the world, and large numbers of individual hobbyists. By then it will probably print multiple materials including conductive ones, so you'll be able to embed circuitry in a widget. Today one of the big killer apps for 3D printers is little action figures based on avatars from Second Life and similar games, but when 3D printers really are ubiquitous, people will move on to far more interesting apps that I can hardly imagine.
Let me not forget this very nice list of a lot of different commercial and hobbyist 3D printers.
Still waiting for my CNC mill platform, the eBay fellow has been getting a huge volume of business and his shop is a bit swamped. I've been getting a bit more organized with the electronics, including resuscitating an old FX2 board design, and I've ordered some stepper motor driver parts that should arrive soon.