I'm pretty surprised to see the military at #5. I know a lot of people believe in what they're doing, no disrespect meant, but I've never gotten the impression that being a soldier is...pleasant.
It would be interesting to see a similar list compiled by Glassdoor (where e.g. Charles Schwab definitely doesn't look like a very happy place to work).
These lists are utterly meaningless. If you go to Google at lower than market rate because "It's Google!" then of course you're going to tell everyone you're so happy. If nothing else, you need to convince yourself because you could have had a lot more money in e.g. the finance industry.
From what I understand, no one at Google is making under market rates. Most likely they could get away with that, but from the salary information posted it seems they pay what most companies trying to hire good software developers pay.