Right but that's really not going to help in most situations. You've never handed your laptop to a friend to quickly check something on the web? It would be i

Right but that's really not going to help in most situations. You've never handed your laptop to a friend to quickly check something on the web? It would be insulting if you were to explicitly logout whenever someone wants to use your computer for a few seconds / minutes. This flaw makes it easy to view passwords in seconds, and makes it easy to do so in an inconspicuous manner. It's a user interface failing more than a security issue.