While I can’t speak for the masses, having a USB stick containing the operating system will be handy when you want to format the computer and require a reinstall. This is definitely a much quicker and more efficient way than downloading, especially for users whose internet may not be reliable or if they’re continuously on the go and may not have a fixed/stable internet connection.
The good news is that Apple has reportedly started shipping the USB sticks containing Mac OS X Lion 10.7 and it will retail for $69, so for those who prefer a physical install, you should be able to purchase the USB sticks pretty soon. Alternatively if you already own Lion but would prefer a physical backup of the operating system, the Lion Recovery Disk Assistant software could be an alternative worth checking out.