I agree that WinCE is a viable alternative to Linux for ebook readers. However, WinCE isn't Windows Mobile or Pocket PC, see
Wikipedia: Windows CE. Like Linux-based devices, a WinCE device can be open to new applications or closed. It is unlikely to run new Windows Mobile applications (e.g. web browsers), but probably can run old WinCE reader applications (e.g. MobiPocket, or eReader, or uBook).