I didn't think there was anything special about the size of the earth (and apparently I'm right). Can anybody explain why this is important, I don't think the article did a very good job of that.
People are probably interested because one of the factors in the Drake equation is the number of Earth-like planets per star.
Too small, and the planet won't be able to retain an atmosphere (e.g. Mars). Too large, and it'll probably retain too much.
I have always been under the impression that the lack of atmosphere on mars was due to its magnetic field weakening and allowing solar winds to carry away the atmosphere over the billions of years.