I'm going to go with the fact that unless you NEVER restart your browser, the likelihood is that you are one or two minor versions behind the latest Chrome code at worst. With Chrome's automagical update system, most users barely notice when an update comes down the pike.
True... however, a moderately large website I have access to analytics has about 5% of Chrome users using something older than 11. It's possible to install Chrome without enabling the auto updates, so exactly which versions of Chrome they still support is somewhat useful information, I guess.
More likely, since the versions of FFx, IE, and Safari they support are the versions of another company's product--unlike their own--they feel like they have to be more upfront.
