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