Because nothing instills fear into the hearts of evil doers like the ancient dreaded art of karaoke!
If your robot is going to sing, you might as well program him to sing well.
Cue the music, Johnny! *sings various Village People songs*
why would a robot have a microphone if it talks out a speaker? put a mic near a speaker, you get feedback. Maybe thats why he sounds so bad when he sings into the mic, it wouldn't be so bad without the feedback.
@Angel85: Maybe the mic or speaker doesn't use magnets so it doesn't create the feedback that normally happens.
Must resist urge to post scientific lecture to correct AMJZero's assumptions