Note: This analysis is not a statement of agreement with their actions, just providing some insight.I am not surprised either but I don't think Sony can be compared with Streisand. From Sony's perspective this makes perfect sense and isn't some emotional over reaction, Someone has gotten around their security and if they don't pursue this it will be seen as an open invitation to hackers on all of Sony's platforms. As a platform company and a content company they're doubly incentivised to pursue these sorts of actions in the courts.
Even the OtherOS debacle makes sense from their perspective. They make a loss on each console they sell[1] and rely on strong games sales to make up the difference. At launch they had a horrible attach rate (games sold per console sold) and much was made of its use as a cheap computing cloud platform. So removing the ability for new consoles[2] to act as a platform apart from its primary gaming role helps Sony's bottom line.
[1] They certainly did at launch not sure if that is the case any longer, historically consoles are sold at a profit once they reach middle age and production costs come down. The Wii was an exception and was sold at a profit from day one, but that is a souped up Gamecube so the factories didn't need much updating.
[2] I haven't updated my console so it can still run Linux for example.