By all means I am not a lawyer, but I have ran an indie studio.
As far as I know you do not need to register a company or LLC in order to sell a game. The only reason you would want to register an LLC is to protect yourself if anyone was to sue you for any reason.
Say for example King comes after you because you are making money off of Candy Rush and it is also a match 3 game. If they decide to sue you and they win then the LLC takes the hit financially. Now if they come at you and win and you do not have an LLC then you take the hit personally.
This is from my own experience and again I am not a lawyer or anything like that so my word is not all knowing lol.