Well, one theory I've heard is that if Libby's sentence is merely commuted and he's still in the appeals process, the case is still open, so if he gets hauled in front of a congressional committee to testify about any of these shenanigans, he can plead the Fifth because his case is still active and he has the right not to incriminate himself. Just because there's less punishment involved, that doesn't mean he's off the hook legally for the crime, just that he doesn't have to go to jail. Once he's pardoned, there's no jeopardy involved in anything he says and he can't take the Fifth. So he'll either have to spill or lie again, this time to Congress. This way Bush and Cheney avoid having their involvement revealed by Scooter in any kind of congressional hearings and Bush can run out the clock and pardon Scooter on the way out. Plus, for the vast majority of the public out there who haven't been paying attention and don't know the legal niceties (see Noah, Timothy) it makes Bush look like he's come to a reasonable compromise, did it out of mercy yet "respected" the court's decision, and wasn't bowing to pressure from the right to completely pardon Scooter. Knowing all this, it's not at all surprising Bush chose that route.
As for the token amount of "punishment" Bush left for Scooter, he won't even feel it. His defense fund headed by Tucker Carlson's dad and Fred Thompson has raised millions of dollars. A $250,000 fine is pocket change. Plus, Scooter comes from money already. He could pay it himself and hardly notice. And it looks like the judge is now saying that the probation was designed to follow incarceration, so if there's no prison there may not be probation unless someone clears this up. Which gives the lie to the fiction put about by the White House and dutifully regurgitated by the media that Bush consulted for weeks and weeks with lawyers and carefully considered what he was doing. This was obviously done quickly on the fly and they didn't research it enough, or they wouldn't have left this kind of legal limbo that's going to drag out this story longer and make Bush and his people look ridiculous.
As to Scooter suffering loss of reputation and career, my sides are still aching from laughter. A glance at the roster of this president's administration will show you just how much criminal behavior holds you back in a Republican administration. With all the Nixon WH veterans and Reagan-Bush Iran-Contra holdovers in this administration, they could hold a corruption convention. And Ollie North is soooo hurting from his wrongdoing. G. Gordon Liddy even sucked it up and went to prison unlike wimpy Scooter and it doesn't seem to have stunted his career growth any. Felony convictions for loyalty and obstruction are probably a badge of honor, a veritable Medal of Freedom, you might say. Noah, are you really that stupid and obtuse or are you actually a brilliant satirist whose work is just too finely drawn for our Philistine brains to comprehend?