I could be wrong, but I believe these portable devices do not change resolutions. Where as a PC can do some hardware switching and handle all the resolution definitions Android and IOS can't. They use a locked resolution and you need to handle the difference between device resolutions by way of software.
Also using a browser to test resolution can give all sorts of inaccurate results. A browser will do what it can to make pages fit if not using browser commands to resize.
I would suggest using CocoonJS to test your resolution as that won't play any resolution tricks on the device.