I like how the iOS screenshots are tiny compared to the Android ones. Making up for much?
To the GP's point, the author is taking advantage of hardware variance and picking larger images.
I think an even more honest way to look at it is that the author uses the Galaxy Neuxs as the Android reference device in all examples, including the screenshots.
This can be defended as a part of Google's effort to try to lead the way for other Android makers with their Nexus series and is probably not motivated by any comparison to iPhone.