From Fedora’s GNOME 3 feature page:

Where has the appearance capplet gone?
GNOME 3 is deemphasizing user customization, or ‘theming’ in favour of a ‘just works’ and ‘slick out of the box’ approach. Therefore, theme changes are no longer exposed in the core configuration UI, except for accessibility themes such as ‘High Contrast’ or ‘Inverse’, which are available in the ‘Universal Access’ panel.

‘Deemphasizing’ is a nice word, isn’t it? Makes sound things so friendly:

The Chinese government is deemphasizing ‘human rights’ or ‘individual freedom’ in favor of a ‘just works’ approach.

Who said I cannot be diplomatic? ;)