I've always wondered about this myself. I think it's funny that they state: "
Note: If you order only the White Wall Tire Paint, you do not need a base coat / primer."
This basically translates to "If you are too cheap to spring for the primer that we recommend then the regular paint will work just fine all by itself."
And then they have a couple weak testimonials. The product is actually pretty inexpensive IMO. It's just a lot harder than most people think to make the white ring totally smooth and round. It's all in the preparation too... like all paint work. I would rough up the area to be painted with a sanding pad or sandpaper and then prop up the bike and spin the tire while holding up the paint brush to it. A couple coats should give a nice thick white line but how long it would last? Who knows.
I've seen a few hot rod guys do it and a couple pictures of old Hondas on the net and they look great. I didn't ask them the name of the product but if you looked up white wall tire paint on the Google you'll probably get a ton of results. This guy came up on top of the Youtube results and he suggests that white wall tires usually have a white strip of rubber under the surrounding black around the white stripe of a tire. I think the Honda tires are white applied to the black tire... not some white rubber layer in the side of the tire. So I don't think his method would work but I haven't tried anything like this.
http://www.youtube.com/watch?v=xkcm3rh60p0