That's hard to believe. Win 8 is supposed to be able to run most of what Win 7 can run.
Anyway, WA's long standing policy is to wait for a new OS to be released before making any needed compatibility changes. For a free app, it is not efficient to spend time and other resources on changes for a pre-release that may need to be changed again for the final release.
Win 7 Home Premium 64-bit SP1, WA Pro 18.104.22.16815, cPro MPxi_remix skin, 5.1 speaker system