What they are talking about here is using boot passwords or encryption passwords, in the case of a duress password it would be for encryption(something like truecrypt). The issue with securing your computer using only a Windows password is your average low level computer guy knows how to get around it, remove it, or bypass it.

Windows has a failsafe built into the OS called the Admin password, your average computer owner doesn't change that, or know how to change it, so with a few keystrokes anyone can enter your system, and look for pretty much anything.

Another way to protect your data which is slightly less obvious than an encrypted windows/duress is the following. It requires a bit more computer savvy, and knowledge of UNIX systems. You duelboot your system and mask your key partition(truecrypt does something similar, but in a very different way). For instance you can use Ubuntu and Windows with your average GRUB loader(it is a boot loader), and mask your Windows partition before traveling, this would allow full access you a working part of your computer, and even if you encrypt your windows partition from Ubuntu you could use terminal to mount the other partition. After traveling you just go in and unmask your main partition, and can load it normally again through GRUB. Using this method it is possible for someone to find your partition, but it requires quite a bit of time, and Unix knowledge, also it looks significantly less suspicious than having a fully encrypted computer.

That being said if your laptop is ever out of your site in hands you don't trust utilize boot and nuke, then fully reformat, just in case anything nasty is added.

I will be upfront, I have not yet had any CBP look at my laptop with the above system, but it tends to confuse every IT person I ever met for 30 plus minutes, and then they are left with an encrypted partition, so should be just fine at the US border.