This week's book giveaway is in the OCAJP forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide 1Z0-808 and have Jeanne Boyarsky & Scott Selikoff 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.