He's buying in early and buying in big in eleven swing states. All the differences are in six figures
http://tpmelectioncentral.talkingpointsmemo.com/2008/08/ad_buyer_mccain_outspending_ob.php
Iowa: McCain has spent roughly $700,000 more than Obama.
Missouri: McCain has spent roughly half a million more than Obama.
Ohio: McCain has spent approximately one million more than Obama.
Pennsylvania: McCain has spent roughly a million and a half more than Obama.
New Hampshire: Spending is about even.
New Mexico: McCain has spent approximately $300,000 more, and has outspent Obama by roughly two to one.
Nevada: McCain has outspent Obama by $800,000, also roughly two to one.
Missouri: McCain has spent $500,000 more than Obama.
Virginia: Obama has spent a million more than McCain, largely because Obama is advertising statewide while McCain is only up in the northern part of the state.
Wisconsin: McCain has spent roughly a half million more than Obama.
North Dakota: Obama has outspent McCain by around $170,000.