I've updated the matrix to state more correctly that "Eclipse.org has only tested" instead of "Eclipse only supports".
That comes from Eclipse release trains plans like http://www.eclipse.org/projects/project-plan.php?planurl=http://www.eclipse.org/eclipse/development/plans/eclipse_project_plan_4_2.xml where only the platforms they actually test on is listed.
It does not mean Eclipse cannot run on Windows 8, it just means the Juno release was not tested on Windows 8 (mainly because it did not exist at the time and
no resources allocated to it).
It should just run fine and we got users using JBoss Tools on Windows 8 according to our usage statistics.
Have you seen any problems running eclipse/JBoss Tools on Windows 8 ?