Best argument from the article imo:

It’s a simple matter of screen real estate. Virtually every modern computer display is widescreen, which is to say it’s wider than it is tall. Websites and web apps, meanwhile, are practically always vertical experiences. Whether you’re on a 13-inch laptop or a 32-inch behemoth of a monitor, the space from top to bottom of your computer is more precious than the space from left to right.