Really?! For the Web Start version, do we need a manifest?
nope. be sure pass the "M" (uppercase) to the jar command to avoid creating a manifest. the JNLP allows you to specify what the main class is.
with this in mind, sometimes distributing with webstart is smaller than distributing standalone JARs.
in addition to fullscreen, most people prefer to sign to get rid of the "Java Application Window" message, which can get in the way of some game graphics if they're drawing directly to the JFrame. (also some classes such as Robot need signing to use)
standalone JARs never ever have the "Java Application Window" message, and never need to be signed to use any classes. so the balance typically is: "I don't need a manifest, but I might need to sign." (webstart) and "I don't need to sign, but I do need a manifest for it to run" (standalone jar)