I downloaded win10 preview and installed on a virtualbox VM running on a Win7 system.
And when i check the Registry entry of Win10 , i see 6.3 as version, but in the screen shot that you provided here it shows 6.4. Which one is correct?
and what would be the Major version, Minor version, Architecture values for the final version of Windows 10 ? Please let us know.

Click image for larger version. 

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I also wrote a piece of C# code in .NET 4.5 just to display the OS versions.
private
voidbutton1_Click(objectsender,EventArgse)
{
label1.Text =
Environment.OSVersion.Version.Major.ToString();
label2.Text =
Environment.OSVersion.Version.Minor.ToString();
label3.Text =
Environment.OSVersion.Version.MajorRevision.ToString();
label4.Text =
Environment.OSVersion.Version.MinorRevision.ToString();
}
And here is the result that I get on the win10 preview and installed on a virtualbox VM running on a Win7 system

Click image for larger version. 

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So it looks like there is no consistency. Please let us know Major version, Minor version, Architecture values for the final version of Windows 10