In Internet Explorer 10, are developer tools not available from [F12]? If so, how do I access them?

No, it has not been removed. The Developer Tools only show up in the Desktop version, not the Metro version.

You can always still use Firebug Lite.

This feature is not available for Metro applications but should still work for Desktop applications.

As an alternative you might want to use Fiddler instead which allows you to at least debug the traffic happening between the Metro browser and the internet. For rendering, it should suffice to check the Desktop version of the browser as they share the renderer, and also have the same JS engine.