Inclusion of style.css

Twenty Fourteen includes its stylesheet through wp_enqueue_style, although you were correct in that wp_head() is required in order for the function to execute correctly.

function twentyfourteen_scripts() {
	// Add Lato font, used in the main stylesheet.
	wp_enqueue_style( 'twentyfourteen-lato', twentyfourteen_font_url(), array(), null );

	// Add Genericons font, used in the main stylesheet.
	wp_enqueue_style( 'genericons', get_template_directory_uri() . '/genericons/genericons.css', array(), '3.0.2' );

	// Load our main stylesheet.
	wp_enqueue_style( 'twentyfourteen-style', get_stylesheet_uri(), array( 'genericons' ) );

	// Load the Internet Explorer specific stylesheet.
	wp_enqueue_style( 'twentyfourteen-ie', get_template_directory_uri() . '/css/ie.css', array( 'twentyfourteen-style', 'genericons' ), '20131205' );
	wp_style_add_data( 'twentyfourteen-ie', 'conditional', 'lt IE 9' );

	if ( is_singular() && comments_open() && get_option( 'thread_comments' ) ) {
		wp_enqueue_script( 'comment-reply' );
	}

	if ( is_singular() && wp_attachment_is_image() ) {
		wp_enqueue_script( 'twentyfourteen-keyboard-image-navigation', get_template_directory_uri() . '/js/keyboard-image-navigation.js', array( 'jquery' ), '20130402' );
	}

	if ( is_active_sidebar( 'sidebar-3' ) ) {
		wp_enqueue_script( 'jquery-masonry' );
	}

	if ( is_front_page() && 'slider' == get_theme_mod( 'featured_content_layout' ) ) {
		wp_enqueue_script( 'twentyfourteen-slider', get_template_directory_uri() . '/js/slider.js', array( 'jquery' ), '20131205', true );
		wp_localize_script( 'twentyfourteen-slider', 'featuredSliderDefaults', array(
			'prevText' => __( 'Previous', 'twentyfourteen' ),
			'nextText' => __( 'Next', 'twentyfourteen' )
		) );
	}

	wp_enqueue_script( 'twentyfourteen-script', get_template_directory_uri() . '/js/functions.js', array( 'jquery' ), '20140319', true );
}
add_action( 'wp_enqueue_scripts', 'twentyfourteen_scripts' );