I've read that defense that he's merely trying to make the extension apply to everyone, but from what I understand (and I'm not a lawyer, so I can only form my opinions based on what lawyers say) that's essentially a lie and a diversion away from their real purpose.
Like I said, the military tends to vote very conservative and Obama just opened up all of the US Armed Forces for homosexuals to serve openly. He's not going to be very popular among the military (I was in the Army when DADT was passed and I expect the reaction to this to be about the same). Also, I remember reading a story back in 2008 about lost absentee ballots from military bases that were never counted. It probably wouldn't have been enough to change the results of the election, but it seems to me that Obama is covering all of the bases to try to ensure that he stays in office.
At this rate, if Obama wins a second term, then I expect him to be working to find a way around the 2-term limit four years from today.