These maps from SurveyUSA don't really give you the full picture. While Ezra notes the final electoral college margins are similar, the margin-of victory in individual states is not. Here's a better look:
Chris Bowers notes that Barack Obama clearly has both a larger base and more potential swing states. To get to 270, Obama simply needs to defend New Hampshire, New Jersey, Pennsylvania, and Michigan, while picking up Ohio, Florida, or two more medium-sized states like Iowa and Virginia. Hillary Clinton has to play defense in the same places, but she also has to spend time and energy defending the Northwest and the Upper Midwest in a way that Barack Obama does not. Her only real pickup opportunities are Ohio, Florida, West Virginia, Arkansas, Iowa, and Missouri. Obama has Ohio, Virginia, Colorado, Nevada, North Carolina, South Carolina, Nebraska, South Dakota, North Dakota, and Texas. Okay, even I don't believe he has a shot at all of those states, but he has a much better chance there than Clinton does in Mississippi or Kentucky or Oklahoma.
In addition, in the states with the ten most competitive Senate races, Obama does better than Clinton in eight of them; only Kentucky and Louisiana are better for Clinton (and, seriously, if Mary Landrieu can't win 25% of the white vote in Louisiana, she's got bigger problems). There's also the third tier of Senate races, in places like North Carolina, Nebraska, Kansas, South Dakota (that's a defense), Texas, and Idaho, where Obama does better in four of five and ties Clinton in the fifth. Should Rick Noriega or Scott Kleeb catch lightning in a bottle, it would be better to have Obama at the top of the ticket. Put Tom Daschle or Ed Rendell as VP and he'll be unstoppable.
At the moment, Barack Obama is the better general election nominee. Period. Full stop. He will have to spend less time defending blue states. He's competitive in a larger number of red states. And he's more competitive in states that have Senate elections. Barack Obama: because this is the year to bust the map wide open.