This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
Yes, only some of them are required in each case. However, there are some devices/emulators which seem to require more than just the ones listed in the spec. The safest thing seems to be to duplicate all the entries in the manifest in the JAD file as well. The complete set of attributes for both the application descriptor and the manifest is found on pp.49-52 of my MIDP book.