Ambrose wasn't on RAW because of what happened between him and Luke Harper at SmackDown. They even said that during a highlight on the show, I believe.
The same may have been done for Daniel Bryan because Sheamus rekt him.
Ziggler, I don't know why.
Although, they also may want more concrete star-power on SmackDown, so it's possible we won't see everyone on both shows all the time. I remember reading they wanted DB to star on SmackDown more in hopes it'll boost SmackDown's ratings.