The White House is only willing to permit aides to be interviewed in private, with no oath and no transcript. To which Congress says, OK, except for the lack of a transcript. As Sen. Arlen Specter (R-PA) argued on the Senate floor earlier this month, they need a transcript in order to hold aides to account for lying. It's a crime to lie to investigators, but without a transcript, it becomes much more difficult to prosecute that crime.
Which, it would seem, is precisely the point. During a backgrounder with reporters today, a "senior administration official" said that the arrangement had been offered in order to "provide information, not to appear to be having testimony without having testimony." False testimony is a crime; whereas false information is, well, lamentable. Transcripts would mean testimony and that would create "a perjury trap" -- I guess in the sense that a liar might get caught.
The official continued soothingly: "misleading Congress is misleading Congress, whether it's under oath or not. And so a transcript may be convenient, but there's no intention to try to avoid telling the truth."
But for some reason, Specter, Senate Judiciary Chairman Patrick Leahy (D-VT), and others just won't trust in the White House's good intentions.