But the larger the build area, the harder it would be to control accurately. If you double each axis, could this printer still hit the previous layer when making thin walls?

You're right but the thing is if you're printing some object that is 5x5 feet you probably don't need 0.5 mm thin walls and if you do need smaller features on a larger design you can print the object with the precision portions directly under the center where you have really fine grained precision and the bulk of the object can still be a couple of feet from the center as long as you don't have a need to print a canoe with 0.5 mm walls.

The resolution will look like the graph of dθ/dx with theta being the angle of deflection of the laser. The plot of the resolution with respect to height and displacement can be seen here: http://www.wolframalpha.com/input/?i=h%2F%28h%5E2+%2B+x%5E2%...

What would be awesome is if they made their model printing software optimize the placement of the model in order to maximize accuracy where it was needed but without putting the laser so close that the outside features are crappy including rotating the model maybe upside down if the more precise portion of the model is on the bottom and it is physically possible to print it that way. That'd be a really interesting software engineering project in my book.

P.S. in case anyone was wondering about the math behind the plot, if you integrate the function for a fixed value of h and take the area from x=0 to h you get pi/4 for any value of h which lines up perfectly for a 45 45 90 triangle.