Google Web History is more useful starting from today because it has support for a new Google service: Book Search. All your queries, all the books you've opened and a list of the pages you've read are available, sorted chronologically. You can also search the books, but only the title is searchable, which is rather weird.
Web History is a service that lets you "view and search across web pages you've visited in the past". The standard version only logs your Google queries and the associated search results you click on, but if you enable web history, Google can track all the pages you visit. This makes your web history persistent (browsers usually keep your history for about 7 days), fully searchable and always available.