As the blog post says, Bigtable internally runs virtually all of Google's big services. This means it's rock solid, and it's not about to get discontinued anytime soon.
Google Wallet for Digital Goods was retired a couple of months back, but they still use it on some Google properties. It's still used for the Chrome Web Store developer fee & I think Android, too. They essentially just made it private.
You might argue that BigTable going through the same thing would be too impactful, but GWDG was quite impactful as well. Businesses that had subscribers paying monthly subscriptions via Google Wallet lost those subscribers.
Are you sure? I'm not a Googler but have been told by other Googlers that Bigtable has essentially been replaced internally (though heard it's still similar). So I wasn't sure how much Bigtable is even used anymore inside of Google.
Of course Google has a whole slew of other storage options optimized for various use cases, but some of these are actually built on top of Bigtable.