Gmail – Does Google use Gmail to discover new links

Yes, a link within a page or a named anchor can be part of a Google search result's snippet

If you try this link - https://www.google.com/search?q=trans+fats

..you will notice that the first result (at least at the time I write) is a Wikipedia article which has additional links within the same result pointing to named anchors within that page including this one - http://en.wikipedia.org/wiki/Trans_fat#Presence_in_food

One of the reasons is so they can do click tracking on what link you clicked, on their search results page. This allows them to detect and optimize their search results.

For example if they noticed everyone that searches for "batman" only ever selects the 2, 3, 6, 7 links, they could remove the 1, 4, 5 links as they are obviously bad results for this search word.

Also you should take a look at Google's search history. I can tell you are logged in from this link and that your search history is being logged. This will give you a good indication of the information that Google collects when you click this link.