I'll take a shot at this: I think G+ is possibly the most comprehensive (in terms of design and functionality) new product in the social space right now. Since it comes from Google, who have the history of "revolutionizing" various aspects of the web, hackers want to learn more and put G+ in perspective of existing (competing?) products. This makes it very interesting not only to read about how to fit G+ into the current framework (Twitter-but-longer? LinkedIn-killer? Facebook-killer?) but also follow the minutiae of the growth, adoption, and evolution of G+ (much like they would have taken to GMail, if the timelines had overlapped, imo).
Google employees care because Larry Page said your bonus depends on the success of social.
I care because if it fails, then it will be demoralizing to the company. Google will quickly become the new Microsoft, where investors and potential hires see the company as a stodgy old company that can't innovate. The press will pounce on google for Google+/Wave/Buzz. Android will be seen as the only bright spot, and even that is out shined by Apple.
If it is successful, then it means that other social businesses aren't nearly as valuable as VCs thought they were. If Google+ is successful, no one is going to pay close to $50B for facebook when it comes time to IPO. It will be the end of the social tech bubble.