Yes, you are right, this seems redundant, but to advanced users it isn't.
'clear on shutdown' => It's more secure in privacy terms, when you close K-M there isn't any trace of your browsing session.
'clear on startup' => This is a litle less secure in privacy terms, when you close K-M all traces of your browsing session are saved. This allows you to recover your session manually (If you forgot to add bookmarks a page you visited and can not remember the url address) from the configuration files where they are stored, as they are not deleted if not start a new session of K-M.
K-Meleon in Spanish