Well, the reality is that today in 2013 the default theme (as confirmed in
Geeklog 2.0.0's comments and just confirmed by myself too by checking admin/install/config-install.php) is Modern_curve which is
not responsive.
Alas, I personally think it looks better for non-mobile users than Denim.
But Denim looks great for mobile users.
Thus I want each audience to get the best experience. Until Modern_curve becomes responsive, I'd want Denim for mobile users.
When it comes to vThemes, I need just 1 global configuration - use Denim for mobiles (you can do so based on small resolutions, if you prefer this method).