$  eix -l|grep "\[U\]"
[U] app-arch/rpm2targz
[U] app-editors/gedit
[U] app-text/build-docbook-catalog
[U] app-text/docbook-xml-dtd
[U] app-text/docbook-xsl-stylesheets
[U] app-text/libspectre
[U] dev-lang/python
[U] dev-lang/swig
[U] dev-libs/libcdio
[U] dev-perl/Compress-Raw-Zlib
[U] dev-perl/Compress-Zlib
[U] dev-perl/IO-Compress-Base
[U] dev-perl/IO-Compress-Zlib
[U] dev-python/pyopengl
[U] dev-util/cmake
[U] gnome-base/gdm
[U] gnome-extra/gnome-system-monitor
[U] gnome-extra/gtkhtml
[U] gnome-extra/yelp
[U] media-gfx/eog
[U] media-libs/musicbrainz
[U] media-libs/swfdec
[U] media-libs/vigra
[U] media-sound/cdparanoia
[U] media-sound/sound-juicer
[U] media-video/ffmpeg
[U] net-analyzer/traceroute
[U] net-libs/gtk-vnc
[U] net-misc/whois
[U] sys-apps/ed
[U] sys-libs/db
[U] sys-libs/gpm
[U] www-client/epiphany
[U] x11-libs/gtksourceview

$ emerge -p --update --deep --with-bdeps=y world

...
[ebuild     U ] app-text/build-docbook-catalog-1.4 [1.2]
[ebuild     U ] app-arch/rpm2targz-9.0.0.3g [9.0-r7]
[ebuild     U ] dev-perl/Compress-Raw-Zlib-2.015 [2.012] USE="-test%"
[ebuild     U ] dev-perl/IO-Compress-Base-2.015 [2.012] USE="-test%"
[ebuild     U ] dev-perl/IO-Compress-Zlib-2.015 [2.012] USE="-test%"
[ebuild     U ] dev-perl/Compress-Zlib-2.015 [2.012] USE="-test%"
[ebuild     U ] sys-apps/ed-1.0 [0.9]
[ebuild     U ] app-text/docbook-xsl-stylesheets-1.74.0 [1.73.2]
[ebuild  N    ] dev-libs/xmlrpc-c-1.14.07-r1  USE="curl cxx"
[ebuild     U ] dev-util/cmake-2.6.1 [2.4.6-r1] USE="-qt4%"
[ebuild     U ] dev-lang/swig-1.3.36 [1.3.34] USE="-octave%"


As you can see, result of eix has vigra, but of emerge still doesn't have.
Also, many of flag U package is excepted from emerge --update.

If so, I think Gentoo's world is not whole world.