Kudos Chris!
That is absolutely correct. For the life of me, I could never really understand why they were classified as Rug Weaver's tools until I saw a few of these so-called tools. They look somewhat similar, but without the knife and hence I can envision some weaver picking up one of these to use. But rest assured, they are definitely a scribe's tool and hence used for writing. I'll follow up with some illustrations on how they are actually used with pictures. As the old cliche goes, a picture is worth a thousand words!
And to add some more visual, I suggest anyone who wants to know more about Palm Leaf Manuscripts and these knives to watch Dr. Perumal's lecture. He is the one of the foremost expert on these tools and Palm Leaf Manuscripts in India. He heads one of the largest Manuscript Libraries in India. The video is available here on youtube, and yes it is in English :
http://www.youtube.com/watch?v=-paJ1ORCHls
Cheers,
Ram