That webpage serves map tiles over HTTP, without asking me to agree to a contract first. I take it that I may therefore access the map tiles over HTTP? Obviously I assume I cannot redistribute them, as they're copyrighted. And it is good netiquette to observe robots.txt for bulk/crawl access. But beyond that I don't believe me visiting their page constitutes me "signing" a contract with Google, any more than Google visiting my page constitutes them "signing" a contract with me.
Perhaps there is some other API with nice JSON stuff and OAuth or whatever, but that's not what I'm talking about. I'm just doing HTTP GET requests for map tile URLs.
https://www.google.com/intl/en_us/help/terms_maps.html
and the first link there is the Google Universal Terms of Service that you also agree to bind yourself to:
It seems very similar in the sense to which Google "agreed" to pay me money if they spider my page more than N times/day, which is what my own website's terms say in the footer. Yet I've never received a check. Is Google playing dumb and claiming they never read the terms, so can't be held liable?
If so, looking at whatever data's on your wire (browsers are subclass of user-agents for a reason), and then doing similar requests by example does not make you sign some agreement with Google, right?
Nope.
To use their API you will need to agree to their TOS
https://developers.google.com/maps/licensing