Office_Black theme is the default theme. It is integrated in the assemblies so we cannot remove it.
Without it you won't see our controls in VS 2010 Designer/Blend and won't be able to edit their default styles (control templates).
Also there is another case - if you want to switch between the two themes? So we cannot remove it.
Plus the theme assemblies are only XAML so their compression ratio is very good.
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