Republicans have made it clear that being the Party of No is their strategy for electoral victory. By obstructing everything in the Senate, Republicans have made everyone and everything about Congress incredibly unpopular. But politics is often a zero-sum game, and making the party in power look like it can't govern is more effective than being a minority party that looks uncompromising. By preventing the Democrats from achieving almost any of their goals, it is clear that Republicans are doing much more damage to Democrats than they are to themselves.
What makes this strategy so effective right now is the political landscape in the Senate. Essentially, no Senate Republican is facing a contest for re-election in 2010. Look at the Cook Political Report ranking of the Senate races, or Nate Silver's rankings. You see there are almost no sitting Republicans in trouble. This creates almost zero political incentive for individual Republican senators to work with Democrats.
It is possible that Democrats might pick up four Senate seats currently held by Republicans--Kentucky, Missouri, Ohio, and New Hampshire--but the Republicans who hold these four seats are all retiring. There are only two Republicans in even minor danger of losing their seats in a general election--Richard Burr (NC) and David Vitter (LA).--and both races currently fall in the "lean Republican" category, and both states are fairly conservative. John McCain faces the legitimate possibility that he could lose his seat, but that would be a result of a primary from his right. That is not the condition that makes McCain inclined to reach across the aisle.
Right now, no Republican in the Senate desperately needs to appeal to the middle by working with Democrats to make themselves look moderate, compromising, and/or sensible. None of them are about to face a tough general election, so they don't fear some amount of disgust from moderate voters at this moment. Most voters don't tend to have long memories in politics, especially low information swing voters. The people in politics that do tend to have a long memories are the donors, activist, and hardcore base voters. This is a group that is happy to see the strategy of obstructionism continue.
What this has done is produce a perfect storm that Democrats in the Senate seem completely unprepared for. Republican have found out that pure obstructionism is a winning political strategy. Stopping the Democrats from governing has done serious damage to the Democratic brand going into the midterms. While this obstructionism strategy might be hurting individual Republican senators, none of them are in tough races, so they don't need to fear what the collective strategy is doing to their individual poll numbers. The Republican Senate caucus rules also produce tighter party cohesion because it gives them the power to punish members that step out of line.
What you have is a simple, winning strategy that I see no reason for Republicans to give up, and no way for Democrats to disrupt by peeling off individual Republicans. Democrats currently can't wield the big stick of threatened GOP losses in the general election against any single Senate Republican to try to convince one to move toward the middle. Democrats might be in control of the Senate, but Republicans are clearly in the driver's seat with the much better negotiating position.
If Democrats don't use means that get around the filibuster, using things like reconciliation, I don't see why Republicans would let a single nonessential bill pass. Even a bill made up of only Republicans ideas could be hard to pass. Letting that happen would make Democrats look more effective and more “centrist.”
This is the inherent problem with a system that lets a minority party effectively bring governing to a halt, and then profit politically from the government being shutdown. This year shows just how much the political environment is responsible for shaping the policy and legislative actions of Congress.