Sorry, I edited as you posted, so I'll repeat it here: I stand by my original point:
If my knitting needle works on an IR eReader, a stylus from any other device should work just as well.
Put a fork in me; I'm done. Come back with a source that says that Sony is using anything beyond IR, and I'll happily admit that I'm wrong. In the meantime, I'm going to go reread
this article.