As a hobbyist that built my own printer I assure you he could've printed it at a better quality then that. Prints can vary wildly in quality, and the price of the machine is largely irreverent (1000$ printers can easily match a 10,000 $ in quality in many cases). He may not've had the most optimal settings for the print.

That said I don't think 3D printing phone cases is worth doing for any reason other then the cool factor. I'd expect 3rd parties to start selling cases for it fairly quickly, there just might not be a huge range of colors/options/prices