There is also the "moon factor" which impacts the earths tilt and also provides other benefits of which I can't recall.
However, even adding all these all conditions, considering the vast number of stars out there, there has got to be a certain percentage of them which have planets capable of sustaining life. But as you and the article imply, that number may be small on a percentage basis.
And then there are alternate dimensions.
The tilt effect is the moderation of swings in axis inclination -- makes for a stable, benign climate. Also, a big moon creates tides, allowing marine life to emerge onto dry land.
Problem is that our Moon is a freak, created during a giant planetary-scale collision 4.5 billion years ago. Although it can happen (clearly), it's not a likely event.
Just watched a program on the Science Channel about that this week. One astronomer made the point that without the moon the Earth would wobble/roll over on its "side" by perhaps as much as 30 or 40 degrees or more, and considering that a measly wobble of 1 degree was responsible for the creation of the Sahara Desert and mass migration of ancient humans, there is no way humans could have survived such climatological instability and evolved the way we have. It seems humans owe their existence to the moon and the extremely, EXTREMELY improbable type of collision that created it.