The policy is temporary. They will roll out support for brand names and other potentially trademark-infringing names eventually. Just for the field trial, they want to make sure that everyone is using their real names because it's less hassle.

To downvoters: straight from the horse's mouth https://plus.google.com/u/0/110295984969329522620/posts/ExKJ... and http://www.pcmag.com/article2/0,2817,2391461,00.asp and https://plus.google.com/105923173045049725307/posts/E3mVj6ns...