I am using the new wdp qualifiers in my application for various phone/tablet sizes. They work for 600, 720, 800, 1200, but not for 1600 and 2560. Google Nexus 10 tablets have 2560 x 1600 resolutions. Why do drawable-w2560dp and drawable-w1600dp not work? How do I define assets for Google Nexus 10?
These qualifiers do not work because the Google Nexus does not fall under them. w2560dp stands for "Width of 2560dp". DP or Density-independent pixels are different than regular pixels. The Nexus 10 may have a resolution of 2560px x 1600px (i.e. pixels) but its dp dimensions are going to be more like 960dp x 720dp (or something like that. I can't give you any exact numbers).
Take a look at these design guidelines for supporting multiple screens to get a feel for the difference between pixels and dp and how you can better design your layouts.