The difference is that we don't allow websites to install third party software on your OS just by convincing the user to click yes on a dialog box - not anymore

The difference is that we don't allow websites to install third party software on your OS just by convincing the user to click yes on a dialog box - not anymore, not after what happened with ActiveX. Also, it's probably not obvious to most users that giving a website access to an innocent-looking USB device is in fact equivalent to giving it full access to their PC.