From a story telling standpoint, there was no reason to have Chekov, Sulu, or even Scotty in there. Uhura was given a more substantial role, but I saw no reason why she should have the same name as the original character.
They were just there because JJ felt Star Trek HAD to have the "whole group." IMHO, without the same actors, there isn't any real reason to have them, unless they were genuinely germain to the plot.
Actually, when you put it that way, I agree with you. When I first heard the early rumours that this was going to Kirk and Spock's origin story, I thought it would be exactly that. The story of Kirk and Spock's first mission. That may actually have been a more interesting story as opposed to all the TOS gang meeting up all at once. Just watch TOS, they don't all meet at the same time. Kirk, Spock, Scotty, and Sulu did. Then McCoy and Uhura arrive later on, and finally Chekov at a later point.