Exactly. The big difference, as I understand it, is that the RNC can spend money to help McCain, but I don't think McCain can spend his own public finance money to help the RNC (i.e. other GOP candidates across the country). The RNC itself has $160 million to spend (as of a few days ago), and help is needed for GOP candidates all over the country. McCain can continue spending his own campaign money in WI.
Wisconsin was one of the closest states in both 2000 and 2004. McCain himself has spent a great deal of time in Wisconsin over the last few weeks. Not only is he fighting for the state, but he has an excellent chance to win it.
$84 million for the entire fall isn't all that much if you remember that the RNC raised $66 million in September alone and much of McCain's money goes to infrastructure, travel, polling, etc. McCain has set up several different vehicles to run ads. Many ads are split down the middle by the RNC and McCain (hence all the ads attacking "Barack Obama and his friends in Congress...") but most are paid for only by the RNC or by the RNC and state Republican parties. For better or for worse, McCain has largely outsourced his political ads to the RNC.