Do you really think that Google is going to be fetching your phone backups, hoping for a wireless password, then driving to your house and connecting to your wifi so that they can... sniff your traffic? Impersonate you on the internet?
Whether or not someone thinks they want to, the question I have is that if you're running a Google O/S, with a good chunk of your stuff available using Google software via Google products, why in the world would Google ever need your wifi password to access your wifi network?
If Google wants to fuck over an Android user (and I'd bet that even Kindle users aren't 100% immune), they almost certainly can. It might be via internally-identified Chrome exploits or something, but I have no doubt they could come up with something.