This is a bit of an odd story from the guys over at The Indy Experience ( cheers Eddie) suggesting that maybe Indy 4 isn't scripted and approved after all:

USA Today was at AFI's tribute to George Lucas last week where they got a chance to speak with both Steven Spielberg and Harrison Ford on the matter of Indiana Jones 4. Spielberg confirmed that writer Jeff Nathanson is preparing an Indy 4 draft for after the Summer...

So it's not written yet? The story was out a little while ago that it was written...oh if they are going to leak information at least let it be the right information! So the script is still being written and will await approval...again. At this rate it'll end up being Bubba Ho-Tep 3!