Earlier quoted context omitted.
Chrome apps can have extensive permissions that web platform does not provide. - Full TCP/UDP socket support (AFAIK this is never coming to the web platform) - Bluetooth support (Web platform is getting this, though) - Filesystem support (e.g. get persistent read/write access to user selected directory. Web platform probably won't get this) Notably the socket and filesystem permissions are not available to extensions…
I will add HID API support, that apps have and extensions don't. https://developer.chrome.com/apps/hid
We would have done an extension but there is no USB HID support. Obviously a web app would be a bad idea. Anyone know if there are plans to make the chrome.hid api available to extensions any time soon?