The full opinion can be found here.
Printers, being used to buying consumables for their offset equipment independent of the equipment manufacturers, have always balked at the idea of being tied to one manufacturer for ink. With inkjet ink exceeding the cost of a good French or Californian bottle of wine, it is certainly understandable that companies are looking for the lowest cost supplier. However, the idea of loosing your warranty if you get caught using cheaper ink has been an effective deterrent and chip coded cartridges have not made it easy to live outside the rules.
Of course, we also know that for a process as complicated as printing (digital, offset or any other variant) to work well, control of the environment is key. How many complaints about print quality have been reduced to paper quality, ink tack or other consumable parameters and how often has an inferior third party spare part with the same geometry (special grease filled bearings come to mind) been found to be the cause of an equipment breakdown?
So, there are clearly two sides to the issue. But with this ruling, printers are now free to wander off the reservation of their HP or Kodak approved supplies and the days of a business concept based on "lifetime margin", giving away the equipment and generating the margin on the revenue stream of supplies, are probably over.
Digital printing equipment is now being treated just as other printing machinery has been treated forever. Chief Justice Roberts used the auto industry as an example where manufacturers cannot control what people can do with a product after the sale.
It will be interesting to see if somebody will challenge the closed "eco systems" like Apple's down the road.