That's the biggest problem with Chromebooks (or at least was the last time I used one).
The thing becomes useless as soon as it stops getting updates, because your browser doesn't get new features and gets locked out of various parts of the internet as time matches on without you. On any other computer, you can keep the browser up to date long after the OS stops receiving patches.
Not sure why I'm getting downvoted. The Chromebook Pixel was an awesome home computer until it stopped getting OS updates, which also pinned it on a version of Chrome that got obsoleted from the web. (Unlike IE, nobody cares if something works in old Chrome, and some sites actively reject old versions for security reasons.)
The thing becomes useless as soon as it stops getting updates, because your browser doesn't get new features and gets locked out of various parts of the internet as time matches on without you. On any other computer, you can keep the browser up to date long after the OS stops receiving patches.