I used to be Director of Sales and Marketing of a U.S. owned and based food manufacturing company that had a Division that manufactured and sold millions of egg rolls and spring rolls to both retail (supermarket) and foodservice venues.

The primary difference between the wrappers of each is the thickness of the wrapper and the diameter of the roll. Spring rolls usually don't weigh more than an ounce... Egg rolls are primarily 3 ounces in weight. Both wrappers are basically made from eggs, flour, oil and salt. There are numerous variations that may include rice flour, etc. Many restaurants purchase wrappers already made and sold in bulk, either frozen or refrigerated, then fill them with their own fillings and usually fry. Frying is preferably done in peanut oil, though good grade oils that can handle high heat are also used.

As I recollect, the biggest selling spring roll was usually a vegetarian roll and the biggest selling egg rolls were usually chicken, with pork a close second.