I think it's that way so the movement matches the orientation of  the doohickeys. Supposedly it makes it easier for beginners who don't care about x,y,z..

Years ago I made a default scene that was set up oriented differently, but it was the Director's view, not Camera view. I lost it somehow and have to make a new one. But there's a bug in Bryce that has never been fixed. Link Sun to view works, but link Clouds to view does not. So if you orient your scene differently the clouds don't look anything like the little thumbnails. Sometimes it doesn't matter, other times it does.

I'm using Bryce 6.1 on a new machine now and it feels so strange going back to the 'old' way.