"I've run this past some folks internally who were surprised to hear that we had ever surfaced reservation names. As far as we can tell, we haven't. Turns out it is a known issue and we're working on it, hopefully will be fixed soon. You may know that last year we started sourcing our own data for the United States, we previously had relied on providers like NavTeq and Teleatlas. Now that we're getting better data, we should be able to turn these labels on.
BTW, you and anyone else can contribute to making sure that we have good data by using Google Map Maker: http://www.google.com/