The votes are there in both houses
The votes are only there if you are counting Republican vs. Democrat. If you count pro-gun voting record vs. anti-gun record vs. no record, the picture is a lot foggier. It isn't necessarily a given that they have the votes.
A second issue is that the bill has to make it out of committee; because they sure don't have the votes to force it to the floor. The committees are controlled by the Democratic leadership.
Historically, the party of the sitting President never does well in the first midterm election. With two exceptions, they have lost seats in Congress every time (Bush in 2002 being one of those exceptions). The Democrats are tantalizingly close to complete control of all three branches of government - just a few votes shy of being able to block filibusters and own the House entirely. So it seems the key issue to me is whether the Democrats want the gold ring or just plan to make the most with the two years they have now.
Both Rahm Emannuel (now Obama Chief of Staff) and Chuck Schumer (Led Democrat Senate Campaign) supported running pro-gun Democrats such as James Webb in order to counter Republican wins in the Appalachia region where Democrats have underperformed in the past. They were willing to let their personal anti-gun sentiments wait so as not to spoil the 2008 election. Will they continue to wait so they can take 2010 as well? I think they will as long as the polling data shows they have a shot. If their popularity dumps though, they may decide to cash out while they are ahead. All of that is a fancy way of saying without the support of Democratic leadership, no AWB makes it to the floor and I am not sure the Democratic leadership is ready to tackle that problem right now.