A different link referring to the same story, but with more specific statements relating to discovery:
http://www.rgj.com/article/20100205/NEWS01/100205026/1004/Report++Philip+Garrido+stopped+having+sex+with+Jaycee+Lee+Dugard+12+years+before+arrest
Of particular interest are paragraph 2 (relating to when sexual activity stopped) and paragraph 4/5 (relating to the nature of the "family unit" in recent years). Both of these allegations were based on documents released by the prosecutor to the defence as part of discovery, so they probably accurately reflect statements given by Jaycee during her LE interviews.
I think that provides some insight into what is going on here. I'll bet that the defence is seeing some level of support and/or empathy in those statements that could be potentially useful in their arguments, and that is the real reason why they want to talk to Jaycee directly. Its the crack in the door. I expect the reason for wanting the videotapes (I'm guessing they have the transcripts) is so that they can read the body language behind what was said, which would be important to know if they do actually get to speak with her.
They are going to have a hard time getting around the primary complaints if she testifies, which, I'm sure, she will, so what strategy does that leave them with? Assuming that insanity fails, the only thing left then would be to mitigate the punishment. That wouldn't do much good for PG, he's going to be in prison for the rest of his life no matter what, but they might be able to save Nancy that way, especially if they can get her off the hook on the assault charges (a real possibility if Jaycee is amiable towards her). I'm assuming that the two girls see their father and stepmother in a positive light and so far we haven't seen anything to suggest otherwise.
Interesting.