What Lexmark lost in court was a case that they brought claiming that the DRM circumvention violated the DMCA. There's no law or case prohibiting printer makers or coffee machine makers from implementing locks like this though.
Ah, yes, that's exactly what I had in mind. So they can't prevent circumvention by law, but they can make it as hard as technically possible.
But as Cory Doctorow points out, DRM can never succeed, because in order to sell a working system to your customer, you have to give them the encrypted content, and the decryption engine, and the key (otherwise, they can't use it). But if your customer is your attacker (or your competitor), you just gave your attacker the encrypted content, the decryption engine, and the key, so now they have everything they need to build compatible cartridges...
I think Keurig's and Lexmark's definition of success might be different than yours though. They don't need the DRM to be unbreakable. They just need to protect their market enough that the benefits (to them) of the DRM exceed the costs.
In the case of digital media, any weakness in the DRM means game over, because file sharing is so easy. But when talking about physical goods like printer ink and coffee capsules, it's a battle at the margins. They just need to discourage enough competition that their business stays profitable.
http://en.wikipedia.org/wiki/Lexmark_Int'l_v._Static_Control...