Michael Kinsley has some wise words on the "grandfather clause" in budget politics. He suspects the Republicans will use it to ensure that budget cuts don't adversely affect anyone today.
I have to note the clause is popular across the board. After Reagan busted PATCO and as union power started to fade, there were lots of deals made with employers which included grandfather clauses. Typically the current employees kept their benefits and salary levels, while new employees started lower with lesser benefits. I believe that's how the UAW handled its negotiations with the automakers in the 1980's and 90's. You can easily find other examples.
It's a shrewd move: the current employees (or beneficiaries of a program in the case of budget fights) are the ones who have the political power; the future employees or beneficiaries may not even know their status. When they do, as someone who might have to work longer before being eligible for social security, the issue is down the road and much harder to get excited about.
But, as Kinsley observes, it's not fair, it's not just.