This decision is the correct one, and it's good that it is being formally recognized as such. I am somewhat surprised it took this long, however. Copyright has little place preventing folks from using, maintaining, and repairing devices they legally purchased, regardless of whether the manufacturer is trying to prevent them from doing so. Cory Doctorow makes an excellent related point, I think:

They have this pretense that DRM is ‘effective’ but then they grant a ‘use exemption’ and assume that people will be able to bypass DRM to make the exempted uses, because they know DRM is a farce...The thing is that there's these two contradictory pretenses: 1. that DRM is an effective means of technical control, even in the absence of legal penalties for breaking it, and; 2. That once you remove the legal stricture on breaking DRM, it will not be hard to accomplish this.

In Groundbreaking Decision, Feds Say Hacking DRM to Fix Your Electronics Is Legal - Motherboard