With the introduction of Windows 8 you can now even choose to install it using a USB flash drive from within the Microsoft Upgrade Assistant. Thankfully, things have moved on and users with a sufficient amount of knowhow have been able to get their copy of Windows onto a USB flash drive and install from it for a little while now. Not too many years ago, before the USB stick came along, if you wanted to clean install Windows, it had to be done using the CD or DVD and an optical drive.
