Magento2 is following semantic versioning. This means that the versions consist of
major.minor.patch numbers. Whenever there are bugs or security issues solved, Magento will release a new "patch" version, meaning an increase of the 3rd and last number.
Magento has said to consider every minor release as an LTS (Long Term Support) release. Which means that every increase of the second number does not mean that support for the previous minor version will be dropped.
So, currently we have Magento 2.0.x and 2.1.x as minor versions. Both of them will be supported for a longer period of time, all though newer minor versions have already been released.
The 2.0.8 and 2.0.9 releases solve issues that exist within the 2.0.x releases. Apparently there are no parallel 2.1.x releases, so these issues probably do not exist in the 2.1.x releases (or will be released all at once in 2.1.1 maybe?).
You could expect more releases like this in the future (2.0.10, 2.0.11, 2.0.12, etc...). Also maybe when 2.2.0 is released, there will still be 2.1.x and 2.0.x releases, until the LTS support of those minor versions will end. As Ben Marks of Magento commented below, the duration of LTS support is 2 years.
Read more about the Magento2 versioning here in the official docs:
Alen Kent has also written a nice blog on the versioning, including all the modules (the