SuperSuper Tuesday

It looks like New York will be joining a growing number of other states which are moving the primary election in 2008 to February 5. So it is very likely that the winners of the primary election will be determined on that day. I have always wonder why there isn't a national primary election. There is a national general election so why not for the primary election. Wouldn't any argument against the national primary election be true for the general election too? What do you think?