The py*-lxml wrapper is not installed with the inkscape package, but is needed for the inkscape html-based user manual.
I checked Inkscape build system, and it doesn't seem to have a hook to build HTML docs right now.
As for docs/keys.*.html, these are already built, but not installed. Maybe it should be also isntalle by the port.
Other than that, I don't see any user manual.
Not sure what's the problem here, but the fix for bug 234797 will add dependency on py-lxml anyway. Help menu works for me.