the open beta client right now is the retail version of it, so you dont need to reinstall the game when it comes out.
http://forums.worldofwarcraft.com/thread.aspx?fn=wow-general&t=680216&s=blizzard&tmp=1#blizzard
http://forums.worldofwarcraft.com/thread.aspx?fn=wow-general&t=680216&s=blizzard&tmp=1#blizzard