See this:
http://blogs.msdn.com/b/chuckw/archive/2013/09/10/manifest-madness.aspxWith Windows 10 VerifyVersionInfo is now subject to the same manifest-based behavior as GetVersion(Ex): by default IsWindows8OrGreater and earlier will return 'true' as expected on Windows 10, but both IsWindows8Point1OrGreater and IsWindows10OrGreater will return 'false' without the appropriate GUIDs present in the <compatibility> section.
So lazarus manifest settings must be updated or you must include your own manifest with these settings if youre using these stuff. Direct3D full-screen applications, High-DPI support including per-monitor scaling or GetVersion(Ex).
GetVersionEx is used in Sysutils unit for win32: CheckWin32Version depend on this. If you want to get the righ OS number you must ensure to update your manifest.
Now I use always my own manifest file, those interested in using this and doing through IDE must report it in bug tracker as new feature request. In the past I recommended the dpi settings and elevation settings.