One thing I don't understand why Walmart hasn't invested in: change the web interface!!! Their website is just not attractive at all!!!
I personally wouldn't say the design aesthetic for either is "attractive", but they're pretty clean and functional, and that is worth a lot. Walmart.com transactions are now a bit easier than Amazon, before you factor in the tremendous amount of effort the latter requires to avoid counterfeits. Walmart.com search is a lot better once you get the right terms, and turn off 3rd parties which they make trivial.