Prosecuting your mom's murderer will not bring your mom back to life.
More often than not, it won't even make you feel any better.
So, is pressing charges only "revenge"...? No. It's justice.
Killing someone's mom is, as you mentioned, an extreme example, but there is no denying that these individuals stole valuable intellectual property, flagrantly violated many individuals' privacy (including a full email log), and illegally compromised an innocent company's systems. These actions are criminal, and not in any trivial way. Though Valve does not stand to gain much or perhaps, any, from possible legal proceedings, that does not mean these criminals should not be brought to justice.
It's not like someone stole your TV, and you want it back because your insurance doesn't cover it. Nothing was stolen. Data was copied. People may have gotten a hold of some of their "secrets", but the cat's out of the bag.
So many people think this way, and it is the reason people who would never try to sneak out of a music store with a few CDs tucked in their jacket, would unhesitatingly pirate a computer game worth much more.
The truth of the information age is that data, which is inherently easily reproducible, has just as much value as tangible goods and that intellectual property can be worth much more than the computer that houses it.
Additionally, the general attitude that hacking and other cyber-crime should go lightly punished (and the reality that it frequently does), have made the internet into a lawless, dangerous place. A casual computer owner, who doesn't always keep every bit of software on his computer patched, runs a very high risk of becoming a victim. Perhaps with more enforcement (like this raid) hackers will think twice before maliciously compromising some stranger's system.
A police officer who tickets a motorist who ran a red light is not compensating the city for any damages, neither is he out for "revenge". The deed is done and nothing can change the motorist's past transgression. So why give the ticket? Simple. Police enforce traffic violations to keep the roads safe. People know traffic regulations are enforced, and so they follow them. Hopefully, cyber-crime will soon be well policed enough to make the internet at least reasonable safe.