Does this remind anybody of the CueCat? Same story...subsidized hardware that hackers repurposed for other uses. I think the makers of CueCat tried to unsuccessfully sue the hackers:
Well CueCat was "free" (Although mostly forced on you). Amazon dash is a regular paid product on Amazon. Neither of them can hold you accountable for hacking/repurposing it. However, if someone has a chance that would be CueCat.
Wifi chips are cheap. So cheap, that I'd all but guarantee they're still making a profit on it, even at $5. You can get ESP8266 chips from people in china for about $2.50 each including shipping, and those will do everything these buttons do. Given Amazon's volume, they probably cost half that for them, so hacking them is pretty much free advertising.
https://en.wikipedia.org/wiki/CueCat
http://www.securityfocus.com/news/89
Do the Amazon Dash buttons come with a license agreement? Has anyone read it to see if it prohibits these kinds of hacks?