Genesis Framework 2.0.1 was mainly a bug fix release for Genesis 2.0.0. It addressed several small bugs and was released two weeks after Genesis 2.0.0.
Genesis Framework 2.0.0 is a major release that includes an option to output in HTML5 with microdata.
Genesis 1.9.2 was the second bug fix release for Genesis 1.9.0. It was expected to be the final release on the 1.9 branch before Genesis 2.0.0 is released.
Genesis 1.9.1 was a bug fix release for Genesis 1.9.0, that addressed an issue with the loading order of child theme style sheets.
Genesis Framework 1.9.0 is a major release and has a completely new front-end design, and some nice improvements for both developers and users.