The Wharton website says that everyone in Wharton graduates with a degree in Economics, so does this mean that everyone there majors in it? And if so, how is it different from the Economics major in the College of Arts and Science? Also, which one is easier to get into and is there any difference in job prospects or internships between the schools?
The undergraduate Wharton degree is called “Bachelor of Science in Economics” for mainly historical reasons (it’s been called that virtually since Wharton was founded as the first collegiate school of business in the world in the 1880s), but also to signal that it includes a significant percentage of liberal arts courses (up to about 40%, depending on the student). But it is NOT actually an Economics degree, as that term is currently understood. To major in Economics, you must be in the College of Arts and Sciences. Wharton’s BS in Economics is really a business degree, more akin to a BBA (Bachelor of Business Administration) than to a BA with a major in Economics.
I’ll let others answer the rest of your questions. 
@dtbd17 “Also, which one is easier to get into and is there any difference in job prospects or internships between the schools?”
The admission rate is slightly lower for Wharton than CAS, but both are very competitive. Students from CAS and Wharton often compete for the same jobs, and internships. I think that the school will not be a major factor in having opportunities. The stronger candidate should be able to win positions whether their resume says Arts and Sciences or Wharton.
While my post is going to go somewhat off-topic, I would like to respond to what Much2learn said. While I agree that CAS and Wharton students often compete for the same jobs/opportunities, the Wharton brand is still more widely known and respected in the business world. Graduating from Wharton would carry more prestige and name recognition with it (a CAS degree is nonetheless very impressive), and it would open more doors, as I have myself experienced.
It’s really just a difference in curriculum, many people from both end up in the same types of positions. The College econ major involves a little more calculus (only one more course) and is 12 credits. The College has a wider range of general requirements, so you would probably take more of a range of classes outside of econ in the College, though both the College and Wharton have mandatory outside the major classes. Wharton has a set of business fundamental classes (such as accounting, operations, marketing, management, finance, etc.) that you have to take. I would say what it comes down to is whether you like straight econ or one of the other sectors of business, and whether you want to take a wider range of classes and have room for a second major or take mainly business classes. The main differences come in the curriculum, and doing some research on the requirements for both would probably help clear things up a little bit more.