Yes, Amazon will surpass Walmart in volume and revenue. Amazon is better positioned as an online innovator to take advantage of new technology and the new generations which take that technology for granted. As online sales of daily goods become commonplace Amazon will have a comparative advantage over traditional retailing even as it moves to add a local presence to its international supply chain. The lack of a large physical footprint will allow Amazon to be more innovative in its effort to supply goods to its customers where they prefer to receive them.
They offer cheaper prices, more items, and the convenience of shopping from home. You don't have to deal with all the lines at Wal-mart, having one cashier open when there's 50+ people in line, and etc. The only downfall is having to wait for the items you bought, if you need something right away then you kinda have to go get it elsewhere.
Amazon is a retail giant in the online community; however, that community is still relatively small compared to the amount of traffic that flows through Walmart's brick and mortar community. Walmart also has a major presence in the online community as well. Along with Walmart's historically low prices, they also offer free shipping to any of their stores for customer pickup. Amazon often times offers free shipping; however, that often involved a minimum sales amount. Amazon has a lofty hill to climb if they wish to overtake Walmart's share of the retail market.
I do not think that Amazon will surpass Walmart. First of all, Amazon is a online business. Walmart is not. Too many people would rather shop on person as well as people who do not know about computers or do not have access to computers. Also many people do not want to have to pay for shipping.