Hi Phanx,
You're right, the tool doesn't detect when an addon is out of date (yet). That's the next feature on the list though!
We're targeting the 0.2-alpha release to switch on our web service which is still under development. This is an alpha release, so the tool is not finished yet. I thought this release might still be valuable though because it makes it really quick and convenient to install addons in one click. It might be helpful for people installing WoW addons for the first time.
Thanks for your suggestions!