How did the "super majority" of 60 come into being in the first place. This is not a rhetorical question; does anyone know?
I believe that this is basically a form of the filibuster rule that has been in place in Congress since the earliest days of the Republic. (If anyone knows any different please let me know.) Filibustering is nothing new. It has been used in the past to block opponents' attempts to enact legislation when the minority was trying to piece together enough fence sitters to stop legislation, or when they were simply trying to wear down the majority. It has been used by both parties in the past and will probably be used again in the future. (I believe that the number to stop a filibuster used to be two-thirds of the Senate, but was dropped to a simple 60 member "supermajority" in the 80's.)
That's not really the problem. The GOP does not want to take away the filibuster as a legitimate parliamentary tool. Instead, they want to limit it to what it was originally for.
After Bush took office in 2000 the Dems used the filibuster for the first time ever to block judicial nominees. That was really unprecedented and was considered a nuclear option when it was first used. The press would have gone NUTS if the GOP had done this - calling them obstructionists, mean-spirited, et al. - but they uttered nary a peep when the Dems actually started doing it.
In 2003, after the GOP won back the majority in the 2002 mid term elections, the idea of using this new nuclear option was discussed among GOP leaders. Frist threatened it a few times, but I believe that he failed to use it because he knew that it was unlikely to pass muster. Too many of the GOP Senators were RINO's and wouldn't go along with it, which would have meant that it would have gone down to defeat and the Republicans would have looked like small-minded losers in even trying to change the rules. (There was also the fear that it might backfire on them in the future if the GOP ever found itself in the minority again - something that seemed possible on November 1, 2004.)
Today things have changed. There are now 55 Republican Senators and 51 of them are pretty loyal partisans and would almost certainly vote for the change. Also, my understanding is that the rules change would only affect votes concerning Presidential nominees. Legislative action would still be governed under the same Senate rules as before.