This is not surprising at all given the Obama campaign's focus on getting their supporters to vote early. As this Reuters article points out, early voting played a key role for the president in 2008:

President Barack Obama and Republican challenger Mitt Romney are neck and neck in opinion polls, but there is one area in which the incumbent appears to have a big advantage: those who have already cast their ballots.

Obama leads Romney by 59 percent to 31 percent among early voters, according to Reuters/Ipsos polling data compiled in recent weeks.

The sample size of early voters is relatively small, but the Democrat's margin is still well above the poll's credibility interval - a measurement of polls' accuracy - of 10 percentage points. (full graphic: bit.ly/RmeEen)

With the November 6 election just more than three weeks away, 7 percent of those surveyed said they had already voted either in person or by mail (full graphic: bit.ly/SWm5YR).

The online poll is another sign that early voting is likely to play a bigger role this year than in 2008, when roughly one in three voters cast a ballot before Election Day. Voting is already under way in some form in at least 40 states.

Both the Obama and Romney teams are urging supporters to vote as soon as possible so the campaigns can focus their door-knocking and phone-calling operations on those who are still undecided or need more prodding to get to the polls.

Early voting was a big part of Obama's victory over Republican John McCain in 2008, and his campaign aims to repeat its success this year.

The Reuters/Ipsos poll indicates the campaign's efforts appear to be paying off, although its advantage could erode as Election Day approaches.

The Obama campaign says it is leading among early voters in Iowa and Ohio, and trailing by a smaller margin than 2008 in several other swing states. It expects its early voting efforts will help the campaign weather a blitz of negative ads expected to saturate the airwaves in battleground states in the final weeks before November 6.

Early voting also partially inoculates a campaign against any late gaffes, although some studies have suggested that early voters are among the most partisan voters who wouldn't be swayed by a mistake by their candidate.

Some have suggested that early voting should be curtailed because it doesn't give the voter a chance to change their mind if circumstances are altered. This may be true, but if it gets people to vote, it's hard to argue against it.