Will all these prosecutions for perjury will have a deletrious effect on the willingness to testify?

Bill Clinton, Martha Stewart, Scooter Libby, now possibly Alberto Gonzales--it's getting to the point that the original crime is no longer the endgame. Instead, it's the means to an end. Look at the effect it's already having: Bush is willing to let people testify, but not under oath, and the Democrats are having none of it. Is this because they wouldn't be able to get a perjury conviction out of it?