Logging out implies that the session has been closed; the next user won't be able to access your data. It may not make much difference to the novice, but experienced users will likely be much more comfortable using the kiosk if they know they can log out.
Your typical user nowadays has email, and logs in to quite a number of other sites, for example facebook, which all have a prominent Log Out link, so it's my belief that the logout link should be instantly recognizable to users.
To use a computer, even, they are required to know about 'logging off'.
I would think user expectation is also important. Is there a long standing user base? They may get confused. Changes to an UI also can always create a situation in which users that have used the particular UI will hesitate because they are somewhat on an autopilot, but the change is throwing that off.
Therefore, you want to think about if this change is really worth it. If you have a small user base, or can communicate the change easily than this is certainly easier.