Ah, I wasn't aware of this. Looks like it was first stocked in Apple stores in January (despite it and other styluses being available well before):
http://www.macrumors.com/2015/01/21/pencil-available-apple-s...
I guess I hadn't asked in a store since then. :)
It's more than a year old now.
And you're deliberately misinterpreting that keynote. Unlike the devices that basically were on the market, you don't need a stylus to navigate the OS or use the device at all.