Another good argument is that a Senate rule which the filibuster is can not override the Constitution which in Article II Section 2 paragraph 2 by not stating a super majority like it does for treaties makes it a simple majority. Why the Republicans are not going this rout after several constitutional scholars have stated this opinion is beyond me.
I believe that honestly there is a general fear of what will happen on both sides of this topic. The right wants the judges in place, but is it worth having the left walk out? The left wants the filibuster protected, but what will be the cost of continuing the fight? Can they afford to walk out, which could possibly cause them votes next year?
Out of this whole topic though, it is senators like Arlen Spector though that I have respect the most. They are following their own hearts and choices in deciding what is right, and are not just going with party lines, regardless of the heat being put on them from their peers.