Why do I need a Chromebook/box?

I'm assuming everyone knows exactly what a Chromebook is, so I'll come straight to the point:

Currently, everything that can be done on a chromebook can be done on the chrome browser(I think it is...by this I mean the browser in windows or mac), so what's the point of getting a chromebook instead of getting a mac or windows and then install chrome. I would be able to do everything the chromebook allows me to do, and tons of features provided exclusively by Windows or Mac(like playing big games offline, or using MS office...web app preview and Google Docs aren't even competitive).

Now, some might argue that "Chromebooks boots in 7 seconds!", or "you can have small individual windows for apps", but still, that would be like adding some dust on the balance, I would not go for the pretty expensive Chromebook for short boot time, or small features that don't really matter. With other desktop OS, there are infinitely many software, changing to Chrome OS means I would be stuck to the web (which isn't at all cheap), and even worse, the extremely limited choice of apps.

I'm fully convinced that Google do make great products, but I just can't come up with any great reasons for me to take the risk. This is why I'm posting this. I want to see if any Verge readers can give me some reasons (probably ones I haven't noticed) that the chromebook is not an useless invention. (By the way, I'm not going to carry two laptops at a time, so don't suggest using this for web only and the other for playing games.)