In any relationship, the party that cares the least about winning an according has the upper hand. That's what you're seeing out of the deficit commission. Republicans don't care about reducing the deficit, so they'll only support a plan that consists entirely (or almost entirely) of spending cuts. If it fails, fine. Most Democrats do want to reduce the deficit, so at least a significant core of them are willing to sign off on a solution that's far from their ideal mix.This is why I have not been too impressed with the notion of a bipartisan deficit commission in the first place. If Democrats want to do something about the deficit, they should do so with the majority they now have, possibly using reconciliation rules in order to circumvent a filibuster. (Admittedly, the Blue Dogs make that problematic.) I realize this idea goes back to Mark Schmitt's theory of how Obama often tries to draw in bad-faith opponents by involving them in the process, and that if they don't have any ideas it's apparent. But the critical ingredient for that to work is public exposure, which does not appear to be a factor in the deficit commission's deliberations.
Ultimately, little will come of this. Democrats will not vote for a plan with significant benefit cuts, and Republicans will not only not vote for anything with defense or spending cuts, but they will even demagogue the benefit cuts as well. The commission's report will most likely be ignored, which is fine from my perspective, as I'm just tired of politicians hiding from accountability by deploying the bipartisanship dodge. I want politicians to get used to actually wielding power and getting held accountable for it, not to look for cover behind a handful of ostensibly dealmaking Republicans who turn around and backstab when convenient, as in the healthcare debate. And while those of us in the know realize that bipartisanship is no guarantee of quality policy, I think lots of voters (especially low-information ones) do believe that.