Yeah, that's a bug with the installer.
There should be no need to uninstall each and every version prior to installing a new version.
Just install the new version over the top of the existing previous version.
And as for the installer bug creating multiple entries in "Programs and Features" instead of updating the existing entry. Until they fix it, you can easily remove an old entry without even going into the Registry. An old, but simple trick is this...
Browse to C:\Program Files (x86)\Stardock or C:\Program Files\Stardock (depending on your version of Windows 8), then rename the "Start8" folder to something else. I just rename it by using an underscore like this: "Start8_".
Now go back to "Programs and Features" and right click (or double click) on an old entry and select, "Uninstall".
Windows will tell you that it cannot find the uninstaller and offer to remove the entry for you. Say yes.
Don't forget to rename the "Start8" folder back to its original name.