Let's say you're a large business, like a major bank, and you have 15,000 people running Chrome. They all come in at 8:30am one morning, turn on their PCs, and the latest version magically installs itself (let's pretend there's some way that a whole bunch of clerical workers who might have access only to an intranet can do this, and that their bandwidth can support 15,000 simultaneous downloads of Chrome at 8:31am). Now, what happens if the latest version of Chrome happens to have a bug that disables some mission-critical web app that this bank uses?

If you're a hacker, you can use Firefox until Google resolves the bug and pushes a new update. But if you're an end user at a bank, your PC is locked down and you can't install another browser (even if you knew how). That little bug in Chrome 26.0.0.1 that got fixed in Chrome 26.0.0.2 the next day could cost the bank millions of dollars as 15,000 people sit at their desks for a day unable to enter transactions.

Businesses like this have to be able to install browsers using a controlled process in which all their web apps get tested with the new version of the browser. And installing a new browser on 15,000 machines takes a lot of IT man-hours (remember, the users don't know how or aren't allowed to install their own software), so there has to be a pretty good justification to upgrade.

Welcome to the grim realities of corporate computing...

By the way, you don't have to be a large bank for something like this to affect you. You could be some tiny business like a real estate broker that depends on a web app but is not big enough to be able to afford a full-time IT staffer to maintain your software for you. I guess my point is that once you're out of the world of software developers, minor problems with browsers can be very costly and upgrading to a new version constantly can be risky.