They sure don't, but it helps if you have an old one lying around. If you want to install Windows 7, you won't be able to use USB3.0. I have both USB2 and USB3 sticks and Windows 7 doesn't install on my friend's PC with either one. Mine, it installed with 2.0.
If you have an optical drive and a DVD, you won't need to worry about this problem at all.
You may think this post is irrelevant since 7 is now old, but that's the case if you want to install it.