Social security...Maybe I'm confused.

Pres. Bush's plan regarding SS includes adding private accounts for people as opposed to the current state of SS which is pooling all the SS taxes into the general fund and then passing out every retired persons share every month. I've heard various estimates of what it would cost the govt. to create these private accounts and it seems to be in the neighborhood of $2,000,000,000,000 (thats 2 trillion) over the next decade. When the shift is all done we end up with retired people getting the same share every month as they do now. I just don't see what the difference is between the old plan and the new. Retirees won't be able to just cash out all their dough as soon as they retire it is just "theirs" and they can control it to a certain extent. I know republicans have always been salivating for private accounts but I just don't see why we should spend so much money to essentially get right back where we started but with a small increase in each person's control over the money. Like I said maybe I'm just confused but hopefully somebody can explain it to me so it makes more sense.