Why would they need to act now? I can't think of a single reason. This isn't affecting them, the negative perception isn't on a market-wide scale, and they haven't even officially announced anything yet.Right now we have two sources vs. zero with no other gaming news outlets giving conflicting reports of this information. Microsoft has said "we don't discuss speculation blah blah". I see no current reason to act is if the 720 not prohibiting second-hand play is likely.
And Microsoft not commenting because it isn't "worth their time" is bullshit. If this is false, every second this goes unaddress is bad for Microsoft.
Consumers know rumours are rumours. If MS announces their Xbox tomorrow and says it will support used games, no damage from erroneous rumours will carry over. Everyone will forget about this shit, and move on. That is why MS doesn't have to say anything. MS is not hurting right now in perception right now outside of fickle and emotional forum members who are not good at reasoning.