Earlier this year, the GOP backed down in the face of the Dems going nuclear. Why not this time? Here's the best answer I've seen:
"It could make the difference for a Republican, in that they no longer have to tag team to break cloture on nominees they want to let through, so there won't be as many ads to run about how 'so and so says they're a conservative, but they voted with Obama 327 times!'" -- Plain blog commenter
This identifies the real reason for the change in the GOP position. It was getting harder for the GOP to stop their own filibusters even when they reached unthinking, foot-stomping stubbornness. So now they've allowed the Dems to render that problem moot. (Update. Bernstein make the same argument here, but it comes from a professional and highly educated political observer.)
No other writer came up with this analysis. The MSM was treating it as no big deal. At the Daily Kos, it was mostly cheers for the defeat of those obstructionist Republicans. HotAir was loud, negative, and scattered. Some pointed out the hypocrisy of the Dems, a few looked forward to using the same power when the GOP reclaims the Senate, a few quoted Limbaugh's laughable analysis that the rules would last only for the Dems' advantage, and then revert. George Will laments the end of a "deliberative" Senate and the beginning of a coarse, 'majority dictates' Senate that is not bound by rules, but by expediency.
RedState had a different take--it wants the end of all cooperation in the Senate in retaliation. The Senate won't pass anything inconvenient like an immigration bill, a farm bill, a continuing resolution--zip. Except that no true conservative trusts the squishy Senate RINOs, certainly not at RedState or HotAir
Thank God for that clear-eyed commenter who understood why the change happened now. In the long run, perhaps George Will will be proven right--we might deeply regret this change. But I don't know a way around it because the Senate has already slid so far down the slope.