You don't see a scroll bar, because there isn't one, since the product list can be scrolled with the mouse wheel.
The update button does exactly that: it checks for an update, so it's always enabled as long the product is installed.
The update buttons in the installer will automatically check for updates at each start, that would be the updater job ( which is the same program, just with a different interface ), the whole point of the installer is that you are control, so it doesn't do anything unless you ask for it so, no automatic update check on start, which is instead done when running it from the updater icon. Remember, it's the same program, it changes its aspect depending which shortcut is starting it.