To be fair to Romney (he's had a bad couple of weeks, I don't want to pile on), this is largely because of how campaign finance law works. You can donate twice to a candidate in an election season, once to a primary election fund and once to a general election fund. Romney's campaign had to borrow money because his primary election fund dried up before he was the official nominee and he could start spending money out of the general election fund. He's still got a bunch of cash on hand in the general election fund.
The GOP slugfest (primary) was long and expensive for Romney, but it is his own fault since his main strategy to stay on top in the primaries was to outspend his competition by huge margins. Obama didn't have a primary challenge but still had donations to his primary election fund, so he was left with all kinds of cash to spend on defining Romney early on before Romney could spend most of his campaign funds.