Mr. Obama should be able "to walk and chew gum" at the same time, but the priority probably should be on walking the government back from the brink of an unprecedented economic disaster that looms in the form of defaulting on our debt, than making great justice for an issue that is somewhat parochial in the eyes of 95% of the population that is supposedly straight.
And the other thing being that while the POTUS has a "bully pulpit" to speak concerning issues of potential interest to his re-election (yes, I'm being cynical) ... any legislation to repeal DOMA and specifically enshrine recognition and protection of marriage equality as federal law starts in the Congress, not at Mr. Obama's desk. Though ultimately, it may end there.
Until then, it remains a state's right to determine (not accounting for any unlikely actions of the SCOTUS to interpret the Constitution as affording equal rights to marriage for all Americans).
That said, NY State passing its marriage equality law will no doubt add considerable moral momentum to marriage equality in many more states.