I have addressed this issue in the WSUS forum and was told that the WSUS team is not responsible for what updates appear in WSUS, that is the responsibility of the specific product group, Windows in this case. I also know at this point that my WSUS is configured correctly.
My users with touchscreen monitors or Surface Pro tablets are eligible for "Update for the English Input Personalization Dictionary - KB2881553" but this update only appears when they bypass my WSUS and go directly to Windows Update. In our environment, we don't want our users launching Windows Update or installing unapproved updates, so this is a problem.
The update appears in the Microsoft Update Catalog, and I can import it manually into WSUS. Unfortunately that is a manual procedure that has to be repeated every time the update is revised, which is several times a month.
It seems that whoever it is at Microsoft who is responsible for Windows updates never ticked the box to "publish this update for WSUS" or similar procedure. Can someone check into this and either fix it or let me know why it's not available?