Although I would agree with you, Captain Gars, seppuku is a bit of an extreme case here. If I were a vassal and my Lord would ask me to commit seppuku for no reason and commit the foolish mistake of still allowing me to walk around freely, I would rebel or defect immediately. If I were a Japanese warlord and my vassal refused to commit seppuku, I would come with my army to raze his castle and have his whole family, children included, crucified.
Most vassals committed suicide on request because they were cornered, and not doing so would mean the annihilation of their whole clan. It's not the same as a vassal refusing to cede this castle or dissolve that army. It's a vassal refusing to die so that his clan lives. It's a direct affront to a Lord's face when he asks "Please die."
Ask repeatedly a Vassal to commit seppuku until he is forced to do so, with no consequence, is a little weird. Even STW2 has leaders immediately becoming ronin or rebelling if they refused to commit suicide for their Lord.