when sprinters are standing on the track, they're sitting. it gives you a more powerful position to start from and allows quicker reaction time on a banked track.
I kind of feel that you can't really trackstand until you can do it while seated. It requires more skill and is more useful as a resting position. But a trackstand is a trackstand. If you can hold the bike still without touching the ground, thats all you need to do for city riding. And standing helps you see over traffic.