I think it defaults to a velocity around 60 so it sounds more realistic (I could be wrong) but you can edit the velocity of individual or groups of notes with Play - Live Playback - Transform (on Sib 7) it might be Play > Transform Live Playback on Sib 6.
You might find more info at the sibelius forum
Legacy Forum Post
about 10 years ago
Okay, thanks. All the insight is great. Please keep it coming!!! :D