It looks like a reveal (shadow) line to me. It is a great look - minimal and simple. However, it is not so simple to do well. It takes a good contractor who can keep things square and level. There is also the issue of wear and tear - without conventional base trim, the drywall can be susceptible to damage from mops, brooms, etc. A similar alternative we often use is to use flush base trim. It's a similar clean look, but can take a little more abuse.

If you and your contractor are up to it, you can find drywall reveal beads here:
http://www.trim-tex.com/product_catalog.php?cat_display=showproduct&id=270
http://www.fryreglet.com/products-reveals.htm

In any event, the lack of an applied base (and quarter-round) help maintain the clean lines of a modern interior. We have used these details in almost all of our projects. Feel free to look for additional examples:
http://www.houzz.com/professional/6066/Eggleston-Farkas-Architects
http://eggfarkarch.com/category/portfolio

Thank you so much for your detailed and thoughtful reply!

What color would you paint a reveal bead if the floor tile and wall are white?

Fantastic. Love the detail