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I find this misleading. It's not really comparing similar situations - Facebook and Twitter started from scratch, while Google already had an enormous user base and one of the most recognizable brands in the world before launching G+ beta.

I totally agree. Google already has 200 million Gmail users. Is it that surprising that they'd be able to get 5% of them to quickly sign up/get invited to Google+?

Not only did Google have an advantage of a large user base. It also got the press coverage from competing with Facebook (FB started as a nobody and had to make a name for itself, Friendster not being this big yet).
Social Media was a term that was widely used and known, Social Networks meant something different.
Google benefits from adopting a proven concept, not being a leading light.
And as it was said before, Buzz was meant to be the Facebook competitor and created some buzz. However it disappeared faster than it appeared.
Let’s wait and see if users are willing to entertain several networks, or if they will leave Facebook in the large numbers required for Google+ to be successful.

Business is business. What does it matter if FB "worked harder" and "started as a nobody." Google took clear advantage of it's decade-long work of establishing an installed base of hundreds of millions of users by leveraging that key asset for new business lines. This is business 101, and a brilliant strategic move by Google, regardless of "merit" on who worked harder or started first.