I don't know, maybe there aren't a whole lot of people who want to use FL Studio for live stuff ... but honestly, live tap-tempo is essential for any workstation, now that more and more 'acoustic' performers are incorporating technology into their live sets.
Also ... there needs to be live audio clip time-stretching (notice how when you're playing a song and you mess with the tempo knob, the pitch of time-synced audio clips changes.
...).