I think most of us would be sad or depressed if our lives were like his. But it seems like he has intentionally conformed the rest of his life to the things that matter most to him (his work, company, personal productivity) rather than what you or I think of as happiness or a good life. I certainly wouldn't want to be him, but if he's living how he wants to live, who am I to judge.
I might be a little biased though, WolframAlpha got me through countless hours of college homework assignments.
I guess it really depends. I think I'd loved this lifestyle - always doing work that contributes directly to humanity's scientific output and having time to follow your own intellectual pursuits? Sign me in.
What's so sad about someone who doesn't really like to spend time outside? Personally I like going outside, but I'm a bit jealous of people who love their work environment that much.
Meetings while walking, and assuming nobody notices? Questioning the practicality of time spent outside? That's kind of... really... sad.