While I agree that the result of the reduced moniker is to shove Walt and what he stood for aside, I doubt that this is the reason. Rather, it is more likely that empty suited meeska mooska louse-keteers consider the name Pixar streamlined along with Disney California Adventure, and are haphazzardly making a consolidated effort to modernize the entire company brand in the same fashion.
This is because noncreatives know how to subtract but not add. I wouldn't be surprized to see them reduce the Walt Disney and Pixar trademarks to "D" and "P" in the future.
Anywho, I had to kind of search for the Disney in the trailer included in the opening post.