>If they'd named it sfo07s13-in-f14.google.com, then browsing to that URL sends google cookies. If it's some server from a recent acquisition that may not be up to Google's level of security, that's dangerous.

Sorry, I'm slightly confused.

I browse newproduct.google.com. My browser calls the DNS, asking for the IP. The IP comes back as 192.168.0.1 [1]. It connects to 192.168.0.1. Gets hit by an XSS, and sends your cookie value to evildoer.example.com.

How would it help you that the reverse-IP of 192.168.0.1 issfo07s13-in-f14.1e100.net? The browser doesn't know that. It thinks its going to newproduct.google.com.

[1]. Yup, that number is just an example.