Much of this is likely posturing. As much as Senate Democrats wanted to pass their Wall Street reform bill by the end of the week, the death of Sen. Robert Byrd (D-WV) Monday morning made that almost impossible. Byrd will lie in state in the Capitol for most of tomorrow, and senators will spend much of Friday at a ceremony in West Virginia, eating up a great amount of the week's remaining Senate floor time. As early as yesterday morning, Senate Whip Dick Durbin told reporters it would be difficult to finish up the bill before July 4, and last night after the conference committee adjourned, legislators suggested very strongly that the vote in the Senate would have to wait.
Likewise House Financial Services Committee Chair Barney Frank--Congress' point man on Wall Street reform--hinted very strongly last night that Brown had given his sign off on the entire package of reforms. The House, Frank said, wouldn't act unless he'd received assurances that the Senate was certain to pass the same bill, and the House is readying to go today.
So there's plenty of reason to suspect this is cant from Brown. But that doesn't make it any less annoying for Democrats.