The first reason is the expense of an Indictment. Those under the gun are not elected officials. Unlike Tom DeLay, and perhaps Karl Rove, for whom the radical right might spring to life, they may not be able to raise a significant amount of outside defense funds. It's one thing to represent someone pre-indictment in a criminal investigation. It's another to represent them post-indictment. I would guess anyone indicted in this case is looking at a minimum of hundreds of thousands of dollars in legal fees. Many will be tempted to cut their losses now, particularly if they can plead to a misdemeanor, rather risk a felony conviction and mortgage their families' future.
The second reason is the Federal Sentencing Guidelines. Even though the Supreme Court ruled earlier this year in Booker v. United States (pdf) that the guidelines are advisory rather than mandatory, judges still must compute the guideline sentencing range and give it substantial weight. The sentencing guidelines for charges like perjury, making a false statement and obstruction of justice most likely will be outside the range of straight probation. The Guidelines provide that some imprisonment is required except for those within Zone A or B of the Sentencing Table.
Check out that sentencing table. Even defendants with no prior convictions can get straight probation only if they are in Zone A, with an offense level between 0 and 8 (computing to a sentence of no more than six months.) If they are in Zone B, with an offense level of 9 or 10 (translating to 4 to 10 or 6 to 12 months) they must spend at least one month on home detention or in a half-way house. If they are in Zone C, with an offense level of 11 or 12 (and a term of 8 to 14 or 10 to 16 months) at least half of the minimum term must be served in prison. Think Martha Stewart.
If they fall anywhere in Zone D, they must serve their sentence in prison - albeit, for this group, that means a Club Fed. Good time only applies to prison sentences of more than 12 months and is limited to 54 days a year, after the first year.
As a corollary and practical matter, the only reduction under the Guidelines that a defendant can count on is one the prosecutor requests in exchange for providing substantial assistance in the investigation or prosecution of someone else. While such deals often are made after indictment, they may not be as sweet as those Fitzgerald offers before indictment. And they won't be available to those who go to trial.
I haven't even included in this calculation the possibility that Fitzgerald is threatening indictments for Espionage Act violations or disclosure of classified information for those who refuse deals. That would raise the stakes even higher.
This is the week that all of the subjects facing Indictment will be faced with their "come to Jesus" moment. Spouses will be telling them to cut their losses and think of the family. They will be forced to juxtapose their loyalty to the Administration with their loyalty to their families and their interest in self-preservation.
My experience tells me that only those who truly believe they are innocent -- and those whom Fitzgerald advises are looking at felonies and jail time even with a deal -- will hold out.
Update: The Velvet Revolution computes the guidelines and says life in prison is possible for RoveGaters.