[FDE] What is the point of this attack?

[Ali, Saqib]

At this year's Blackhat, Ms. Rutkowska  will demonstrate an attack
which allows you to bypass Vista's BitLocker .
http://www.tgdaily.com/content/view/31858/108/

But I am not sure sure what is the point for this attack?  Seems like
you have to be already logged in into the system to install the
rootkit. If you are already logged into the system that means you have
already bypassed the BitLocker authentication..... So why do you need
to install the rootkit????