xev says this when I press the button:
KeyRelease event, serial 40, synthetic NO, window 0x5c00001,
    root 0xc4, subw 0x0, time 948395, (184,555), root:(1696,581),
    state 0x0, keycode 150 (keysym 0x1008ff2f, XF86Sleep), same_screen YES,
    XLookupString gives 0 bytes: 
    XFilterEvent returns: False

dbus-monitor:
signal sender=:1.6 -> dest=(null destination) serial=1404 path=/component/kded; interface=org.kde.kglobalaccel.Component; member=globalShortcutPressed
   string "kded"
   string "Sleep"
   int64 970492

dbus-monitor --system says nothing.

I use Kde:Distro:Factory repository:
bundle-lang-kde-cs-12.2-4.9.noarch
dbus-1-qt3-0.62-238.8.x86_64
kdeartwork4-wallpapers-4.9.1-184.2.noarch
kdeartwork4-wallpapers-weather-4.9.1-184.2.noarch
kdebase4-libkonq-4.9.1-300.2.x86_64
kdebase4-openSUSE-12.2-159.14.x86_64
kdebase4-openSUSE-lang-12.2-159.14.noarch
kdebase4-runtime-4.9.1-382.1.x86_64
kdebase4-runtime-branding-openSUSE-12.2-159.14.x86_64
kdebase4-session-4.9.1-58.1.noarch
kdebase4-workspace-4.9.1-772.1.x86_64
kdebase4-workspace-branding-upstream-4.9.1-772.1.x86_64
kdebase4-workspace-ksysguardd-4.9.1-772.1.x86_64
kdebase4-workspace-liboxygenstyle-4.9.1-772.1.x86_64
kdebase4-workspace-plasma-calendar-4.9.1-772.1.x86_64
kdebase4-workspace-plasma-engine-akonadi-4.9.1-772.1.x86_64
kdelibs3-3.5.10-65.34.x86_64
kdelibs3-default-style-3.5.10-65.34.x86_64
kdelibs4-4.9.1-506.2.x86_64
kdelibs4-branding-upstream-4.9.1-506.2.x86_64
kdelibs4-core-4.9.1-506.2.x86_64
kdenlive-0.9.2-22.5.x86_64
kdenlive-lang-0.9.2-1.1.noarch
kdepimlibs4-4.9.1-288.2.x86_64
kdepim4-runtime-4.9.1-145.2.x86_64
kde4-filesystem-4.9.1-184.1.x86_64
kde4-kgreeter-plugins-4.9.1-772.1.x86_64
kde4-l10n-cs-4.8.5-205.9.noarch
libdbusmenu-qt2-0.9.2-3.5.x86_64
libdbus-1-qt3-0-0.8.1-83.4.x86_64
libkdecore4-4.9.1-506.2.x86_64
libkdeedu4-data-4.9.1-37.2.noarch
libkdepimlibs4-4.9.1-288.2.x86_64
libkdepim4-4.9.1-354.2.x86_64
libkde4-4.9.1-506.2.x86_64
liblockdev1-1.0.3_git201003141408-21.4.x86_64
liblockdev1-32bit-1.0.3_git201003141408-21.4.x86_64
libpolkit-qt-1-1-0.99.1-52.7.x86_64
libpoppler-qt4-3-0.18.4-2.3.x86_64
libpoppler-qt4-4-0.20.2-2.1.x86_64
libproxy1-config-kde4-0.4.7-15.6.x86_64
libqt4-4.8.2-2.1.x86_64
libqt4-devel-4.8.1-1.2.x86_64
libqt4-qt3support-4.8.2-2.1.x86_64
libqt4-qt3support-32bit-4.8.2-2.1.x86_64
libqt4-sql-4.8.2-2.1.x86_64
libqt4-sql-mysql-4.8.2-2.1.x86_64
libqt4-sql-mysql-32bit-4.8.2-2.1.x86_64
libqt4-sql-sqlite-4.8.2-2.1.x86_64
libqt4-sql-32bit-4.8.2-2.1.x86_64
libqt4-x11-4.8.2-2.1.x86_64
libqt4-x11-32bit-4.8.2-2.1.x86_64
libqt4-32bit-4.8.2-2.1.x86_64
libyui-qt-pkg4-2.42.2-1.1.x86_64
libyui-qt4-2.42.2-1.1.x86_64
lockdev-1.0.3_git201003141408-21.4.x86_64
mozilla-kde4-integration-0.6.4-1.1.x86_64
pinentry-qt-0.8.1-17.3.x86_64
polkit-kde-agent-1-0.99.0-25.10.x86_64
polkit-kde-kcmmodules-1-0.98.1+git20110929-16.11.x86_64
python-kde4-4.9.1-34.3.x86_64
python-qt4-4.9.4-1.14.x86_64
qtcurve-gtk2-1.8.15-3.4.x86_64
qtcurve-kde4-1.8.14-55.4.x86_64
qt3-3.3.8c-121.2.x86_64
texlive-qpxqtx-2012.52.svn15878-1.10.noarch
tomahawk-kde-0.5.5-21.1.x86_64
yast2-control-center-qt-2.22.2-3.4.x86_64
yast2-qt-branding-openSUSE-12.2-17.26.noarch

This is a problem with systemd. Systemd-44 does not have org.freedesktop.login1.Manager.Suspend yet. Thus upowerd fails:
# /usr/bin/gdbus call --system --dest org.freedesktop.login1 --object-path /org/freedesktop/login1 --method org.freedesktop.login1.Manager.Suspend true
Error: GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: Method "Suspend" with signature "b" on interface "org.freedesktop.login1.Manager" doesn't exist

Downgrading upower to 0.9.16 fixes the problem of course. This version did not have systemd suspend support yet.

The systemd support was not explicitly disabled at build time, and sneaked in that way.

*** This bug has been marked as a duplicate of bug 780709 ***