Expression Design is supposed to be able to import and export PSD files. PSD is one of the more common file formats, because it is the one that Photoshop uses.
However, the import capability that Expression Design has is limited to... getting the embedded bitmap inside the PSD file. That one is supposed to let you get a thumbnail over PSD files, not as an import tool.
The problem with that is that PSD files are not bitmaps, they are composed of layers, transforms, and a host of other things that I am probably forgetting. Saying that you can import a PSD file by just importing the bitmap is effectively lying.It may be true in the strict sense of the word, but it is misleading by not specifying that the comparability is so limited as to be useless.