All other packages seem to do so. dev-util/ninja-1.7.1 (doc ? app-text/asciidoc) dev-vcs/git-2.10.0 (doc ? app-text/asciidoc) sys-fs/btrfs-progs-4.7.2 (>=app-text/asciidoc-8.6.0) x11-base/xorg-server-1.18.4 (doc ? app-text/asciidoc) x11-libs/libICE-1.0.9 (doc ? app-text/asciidoc) x11-libs/libSM-1.2.2-r1 (doc ? app-text/asciidoc) x11-libs/libX11-1.6.3 (doc ? app-text/asciidoc) x11-libs/libXaw-1.0.13 (doc ? app-text/asciidoc) x11-libs/libXcomposite-0.4.4-r1 (doc ? app-text/asciidoc) x11-libs/libXdmcp-1.1.2-r1 (doc ? app-text/asciidoc) x11-libs/libXext-1.3.3 (doc ? app-text/asciidoc) x11-libs/libXfont-1.5.2 (doc ? app-text/asciidoc) x11-libs/libXi-1.7.6 (doc ? app-text/asciidoc) x11-libs/libXmu-1.1.2 (doc ? app-text/asciidoc) x11-libs/libXtst-1.2.2 (doc ? app-text/asciidoc) x11-libs/libxcb-1.12 (doc ? app-text/asciidoc) x11-libs/xcb-util-0.4.0 (doc ? app-text/asciidoc) x11-libs/xcb-util-cursor-0.1.3-r1 (doc ? app-text/asciidoc) x11-libs/xcb-util-image-0.4.0 (doc ? app-text/asciidoc) x11-libs/xcb-util-keysyms-0.4.0 (doc ? app-text/asciidoc) x11-libs/xcb-util-renderutil-0.3.9-r1 (doc ? app-text/asciidoc) x11-libs/xcb-util-wm-0.4.1-r1 (doc ? app-text/asciidoc) x11-libs/xtrans-1.3.5 (doc ? app-text/asciidoc) x11-proto/fontsproto-2.1.3 (doc ? app-text/asciidoc) x11-proto/recordproto-1.14.2-r1 (doc ? app-text/asciidoc) x11-proto/scrnsaverproto-1.2.2-r1 (doc ? app-text/asciidoc) x11-proto/xextproto-7.3.0 (doc ? app-text/asciidoc) x11-proto/xproto-7.0.29 (doc ? app-text/asciidoc)
> All other packages seem to do so. That's not true at all. There are many ebuilds in the tree that depend on it unconditionally.