glGetIntegerv(GL_DEPTH_BITS, &DepthBits);
I think you are supposed to use glGetFramebufferAttachmentParameteriv with FRAMEBUFFER_ATTACHMENT_DEPTH_SIZE as param (although I haven’t yet figured out how to get it to work with the default framebuffer on AMD 11.2).
I also have failed to query the default framebuffer and I wonder if this a bug or intentional.
Meanwhile you can use WGL, XGL, EGL or whatever you used to create the default framebuffer, to check what depth etc. you got.